I'd like to say this about Sarpadia and Sarpadians: I think there's ample evidence that humanoid civilization on/around Sarpadia isn't extinct. Here are my evidences, other than the Weatherlight red-shirt.
1) Somebody wrote and reads the volumes of
Sarpadian Empires. True, the source could be a foreign scholar, but given the geographic isolation of Sarpadia, this registers as unlikely to me. If it was a planeswalker, it wasn't Tev Loneglade, considering he went off his rocker before the end. And when he did, he wasn't opposed (that we know of) by the actions of another Planeswalker, casting doubt on the idea that there was one there, especially given the nature of the Shard of Twelve Worlds, we should have seen the Chronicler if they were a 'walker and spared for that reason. You could say that the books might trace to Guff's library, but I think that's kind of a last resort. All in all this suggests the survival of Sarpadian culture that can be perused and appreciated by later generations.
2)
Sarpadian Empires, Vol. VII. The past lives in its pages, waiting to come again, but the tokens it creates are all the tokens of the "barbarian" factions that overthrew the Empires -- Goblins (over dwarves), Thrulls (over Ebon Hand), Camarids (Homarids over Merfolk), and Saprolings (Thallids over Elves). The white citizens are a little out but the Icatian internal crisis is human versus human, Citizens fit both sides. If the present of Sarpadia belongs to these factions, or the Thrulls in particular, why are they what's conjured through time, rather than the lost?
3)
Icatian Crier. The rifts typically didn't displace objects in space very much, and the fact that she has appeared in the ruins of an
Icatian Town suggest this is true: she's still on Sarpadia, in the Rift era. However, her news of war has not lost its relevance, suggesting that there are still people that the news can reach, to be warned of impending doom (different, unrelated war and doom) and not just an endless mass of hostile Thrulls. For her news to be relevant, there must be a recipient.
4) Combined with the first fact, the fact that the Thrulls suggested in the "Total thrull victory" theory didn't leave Sarpadia. The Thrulls were smart, if their marks could escape via boats, there's no reason to believe the Thrulls themselves couldn't devise sea travel. Especially with the Homarids (as per Homarid Shaman) providing rivalry to the land, the Thrulls have reason to mess with water. So if they didn't, that suggests they aren't an omindestructive swarm.
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All in all, it seems that a culture with scholarly ability and an Icatian cultural heritage likely exists with access to the Sarpadian mainland in the Rift era.
However, we know the Empires fell. It would be somewhat disrespectful to FE to suggest otherwise. What, then, were there fates that brought us here
Dwarves: The dwarves do seem to be extinct, utterly exterminated by the Orcs & Goblins before the empires fully fell. Multiple flavor texts from FE itself attest or seem to attest the end of dwarvendom, with the records of the dwarves themselves being in mass graves and ruins, while they otherwise pass into myth and legend. The text on the Randy Asplund-Faith Dwarven Soldier is perhaps the most indicative: If there is a legend among present-day dwarves that the dwarves of Sarpadia will one day return, it suggests the dwarves of Sarpadia are gone as of the time of the legend. As a child I always had the crack theory that the blue dwarves from
Apoclaypse who show up and save the day by applying lava to the Stronghold may have been the fulfillment of that legend, but I don't think the evidence actually bears that out.
Voldalians: The Voldalians buggered off; their fate is fairly well recorded with their late arrival in Etlan Shiis. As for the Homarids themselves, we know they're still around throughout Dominaria, but given their favored climate
Elves: The elves are the most uncertain. Their particular foe, the thallids, are only questionably sapient, but also had the numbers and force to push the elves over the brink and at least dissolve their empire. Did an elven population survive in a reduced state? There's no particular evidence of them being deliberately hunted down and finished off, but Havenwood is absolutely known to have been overrun, and it would, in my mind, be completely up to the interpretation of any later author whether or not a stable population survived anywhere.
Homarid Shaman's flavor text suggests that some Havenwood elves at least lasted long enough to write sad records about the ruin of Havenwood (and not just to the Thallids, it seems)
Ebon Hand: Whether any Tourach-worship survived, the Ebon Hand as it was was crushed by the Thrull Rebellion. Honestly, it seems possible that the Thrulls may still maintain the faith of their creator-oppressors, though equally possible that they would ditch it.
Icatia: The Icatians are the group we have the best evidence of survival for, yet paradoxically it's arguably the most important that Icatia, as a civilization, crumbled. What then? Well, when the Roman Empire fell, it didn't mean every Roman citizen died, but a lot of them stopped being Romans because the empire didn't exist. And then for hundreds of years, successor states claimed the legacy of their great forebearer. I think that's probably the fate of Icatia. Ailis Connaut, the knighted scout, lived long enough to see children of her generation become adults before Icatia properly fell, and to her at least something of great value and beauty was lost in Icatia's final end. I would personally suggest, and feel that the evidence bears out, that Icatian successor states came from cities, colonies, and otherwise populations that became cut off from one another between the fall of centers like Trokair and the collapse of Icatia's central government and their capitol. Also to be considered is the internal strife: some of these settlements would violently reject others on the Farrelite divide, meaning that once a crisis of succession occurred, there wouldn't be a single claimant. That could easily prevent Icatia from re-forming as a nation once the collapse began, leading to scattered survivor groups that identify as Icatian, but can't really be said to be the nation of Icatia.
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At this point, I speculate freely
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The biggest question, if we are to reject the "Everything is thrulls" result, as I believe we have evidence to do, is "Why isn't everything thrulls?" But here is what I find to be the biggest likely controlling factor on the Thrulls: They are sapient. Everything suggests that the later generation of Thrulls, that organized and led the rebellion, are of at least human intelligence. They may even have forms specialized for intelligence. They can communicate and build their own society and culture, one that seems to be most strongly based on their own freedom and self-determination. So, would they necessarily come into conflict with the Icatian surviors? On one hand, the Icatians are humans, as were the Ebon Hand cultists. On the other hand, if the Thrulls have theological understanding, they could know that Icatian humans aren't followers of Tourach and the Ebon hand, or even that they (the thrulls) and the Icatians have a common enemy in the Ebon Hand. On the other side, Thrulls are creepy and frightening, an Icatian soldier's first instinct would probably be to stab the horrid thing, and that could well sour relations. But the Icatians are in no state to go thrull stabbing, as they have to worry about the Orc and Goblin raids one one side and dwindling resources on the other. The Orcs, on the other hand, are very strong, and looking for fresh meat. They absolutely would, I think, attack Thrull groups. And thallids. And basically anything else they can attack alongside Icatian survivors and the dwarves they wrapped up early. This makes the Orcs a main mutual war front.
I actually think this could be a novel and interesting direction: the thrulls are intelligent. Nothing is stopping them from being intellectual or even diplomatic. Creatures bred to die came to see the value in their own lives and threw off their murderous oppressors, is it too much of a stretch to think that they evolved empathy?
I would personally guess that the Thrulls became a preeminent power on Sarpadia, but not the universal hegemon. Containment against the Orcs would be hard fought, and the humans and any elven survivors would be struggling to survive against the climate more than they'd be able to make trouble for thrulls. The equilibrium state of Sarpadia's land is an advanced thrull society, a smattering of post-Icatian city states, and finally a breakdown of the Orcish forces running out of steam and/or turning on each other. The elves might or might not be dead, but the Thallids certainly survive given how they're found in later eras and certainly "control" what used to be Havenwood. Naturally, the strength of these forces can shift with the resources available, waning in the depths of the Ice Age and the Rift Era, waxing between the two and now. Especially if, like Otaria, Sarpadia was spared the worst of the Invasion, it could have rebuilt quite a bit at that time.
Nowadays, what remains? Probably a number of city-states rising out of the ashes of the Rift Era, all of which claim to be the inheritors of old Icatia's glory but none of which really have the force to unify humanity. Scattered elf populations, surviving hidden away. Creepy forests full of Thallid overgrowth. Starving orcs scratching their living from rocks and howling at rage from the mountains and the hollow, echoing halls of dwarves millennia dead. A Thrull society, fundamentally inhuman but possessing a core reasonable humanity, which may have gone through its own divisions in the intervening years as new minds write new values in new tablets and discover new ideologies and mutations. Waters where Homarids practice their inscrutable ways. Depending on just what a refined, modern-era thrull society looks like, this is a continent that (consistent with Fallen Empires) seems a harsher and less civilized place than the rest of Dominaria, sort of an alpine Sword-and-sandal theme, recalling Robert E. Howard's hyperborea. A place dominated by the ruins of what was and has no place to be again, but for itself very much alive.