Been doing some homework on this issue, but I believe if any of the big three were to file chapter 11, they are legally not obligated to honor old debts or warranties prior to chapter 11.
BUT, here is the BIG BUT, it doesn't mean they can't do it still, because of the importance of not wanting to lose patronage. The bankruptcy courts understand this inherent value, and so do creditors. So my point is, in the circumstance that either of these big three hit the curb, it doesn't mean you warranties are dead automatically. In the short-term after the bankruptcy you might run into some issues, but I think in the long term, I am pretty certain your warranties will remain intact.
If anyone sees any holes with this feel free to add, I don't want to mislead.