I understand that. But Stitch survived the vacuum of space with no problems. And got blown up in a volcano, and survived re-entry(or crashed a space ship from space, can't remember).
If he can be killed, it won't be easy, even for Hulk. Severely beaten I'll give you, but him just outright killing him I have a hard time seeing, especially since Stitch is made out of all these uber tough polymers and stuff to prevent just such a thing from happening.