[spoiler] um...Could we not just have come back for him?

[Abion47]

I find it odd that reading through this whole discussion, no one has mentioned this fact.

Suppose Simon-3 left Simon-2 on the plateau. Suppose that, after it all, he decided to go back up. And suppose that, somehow, he manages to find another Omnitool, make it all the way back from Phi to Tau through the collapsed cargo tunnel or the destroyed Alpha, then successfully navigates the darkness from Tau to the climber, ascends to Omicron, and meets with Simon-2.

Then what? You would have two Simons, more identical than even the most genetically similar twins ever born, meeting face-to-face. And if the whole paradoxical event didn't make things awkward enough, there's still the fact that Simon-3 left Simon-2 to rot, continuing forward with the then-knowledge that he would live happily on the Ark while his doppelganger spent his days trapped in a living hell. Given how Simon-3 reacted to what Catherine did, what makes you think that, if the Simons met back up, they would be instant friends?

And even that is all assuming that the battery packs on either Simon doesn't run out of juice during all this. When that happens, the cortex chip will stop functioning, leaving the minds of either Simon in suspended time, while the structure gel hardens and becomes useless.