He does, in theory, but that all takes place after the final Battle. The epilogue, endings and Satoshi's ultimate fate however were never decided to be a necessary part of that. The conclusion of the final battle is just as valid an ending as the rest.
How can he both die "in theory" and also live?
entropy in this case being the collapse of the universe leaving only the zero point or the root left.
That's not entropy, though. In fact, I believe the collapse of the universe (in a Big Crunch) is one of the few situations in which the entropy of the universe actually could decrease. The heat death of the universe (which is the path increasing entropy inevitably leads to) will not result in an empty universe, but rather one that is a sea of fundamental particles at a uniform temperature (where no chemical reactions or other methods of extracting energy from the surroundings to enable a local entropy decrease are possible, and thus life cannot exist).
again it was supposed to be decided by the readers. There's fifty plus endings to the story if memory serves. Sadly due to trolling it's not possible to have readers decide on an ending together.
Well, yeah....
I'm not convinced "reader-decided endings" is that great an idea anyway. It would probably just end up horribly grimdark and with Sakura dying horribly or something like that....
Also, how does that fit with the "entropy" thing? If he's always fated to die (well, everyone is eventually, precisely for entropic reasons (i.e. the state of being dead has a lot more ways of existing than the state of being 'you' does, so given enough time you will always transition to the "dead" state)), how can he have endings in which he doesn't?