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

[WALP]

Also she broke mid-sentence, my understanding of it is also that she didn't commit suicide, but the hardware malfunctioned, perhaps due to the ocean pressure.

Simon-3 could accept it more easily after being copied, because he wasn't the one being left to die, he was being selfish and the reality only struck him after HE would have to be left behind after launching the Ark.
I think he believed he would be the lucky one and his copy would just have to deal with the consequences.

But how is Simon-2 left to die if they can just come back for him?

---

Yeah... at first I wanted to reply to the original post in here but then I saw that most of the things I wanted to say were already answered (Simon-3 being stuck down there, Simon-3 understood the concept of copying only after he experienced it from the Simon-2 fiasco but Simon-2 wouldn't understand).

As to how Simon-3 could maybe still get back to Simon-2... well, it could work. IF he finds some structure gel, which then works its magic on the Omnitool and/or Catherine's chip. He could then open the airlock, find his way back to the climber and ride it back up to Omicron.

He does not specifically need Cathrine's chip or omnitool. All of the people who are dead in abyss/tau/phi could only get down there if at least one of them had an omnitool with access to the climber and sites down there.

Regardless he has plenty of structure gel all over his "own" body, so if he can lose an arm, he can also share a bit with Cathrine's omnitool. it should really not need that much gel.