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

[hollowleviathan]

Even if you picked the option to, you didn't really kill Simon-2, you just drained his battery so he doesn't wake up. He's not otherwise damaged, and the station clearly still has power so you could either re-charge the battery or find him a new one once you get back. Heck, you could stick Catherine's cortex chip in that body replacing Simon-2 if you like. She'd surely to able to repair the Omni-tool.

The trip back up is hazardous with the leviathan etc, but I think it's still possible, nothing is broken irrevocably that he needs to get back up. Simon-3 has a lot of time on his hands, he can just wait for the Abyss currents to calm down if he wants.

Sure, there are horrors awaiting outside the door, but honestly, they could just slip out the door for the abyss and start walking up the ocean floor to the surface. Why not? If I had 100s of years, I'd want to see if there were any bunkers of survivors. WAU might even calm down if you can start up (real or simulated) signals from the surface that humanity is preserved.