I have not had the deathtouch creature with the Lead side of the card combo yet, so I do not know for sure if it will kill all blockers. I thought it would. If I get the combo with the rat, I will post my results here.
It shouldn't work, if it does it's a bug. But if you want it's easy to test, just ask for someone on the Discord to test it out against, make sure you get a starting hand that can play the rat, and that they get a hand with at least two 1 power creatures, and then simply attack and have them double block it.
Do note that even if deathtouch should happen to be bugged, which I'm pretty sure it's not,
Rancid Rats is not the best way to get a board wipe using
Destined // Lead, since skulk will prevent most creatures from blocking it.