There's a lot of precedent in SW, both in-canon and in Legends, for characters surviving things that they shouldn't logically be able to survive. As stated above, Anakin was human, yet he survived having his limbs hacked off and having his entire body burned to a crisp by lava. Luke survived a fall on Bespin that should have logically killed him (especially after the beating that Vader had given him beforehand). So an alien like Maul, who's biology might be different from humans anyway, yeah it's not terribly hard to buy. Also killing him off in TPM was a mistake to begin with imo.