From what I remember, they don't really go into that in the books.
Also, I'm not changing my vote, but I will give an example of Alex's nigh indestructibility...
Survived a nuke and regenerated himself back from a bit of tissue the size of a worm. Theoretically, if one cell survives and has access to other organic matter, Alex survives, but again, that's only theory.
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Me as a bunny slug by Nio
http://img.imgcake.com/nio/21raydynpngan.png