I really couldn't swallow the idea that Lawrence would forgive him for, what she sees as essentially murdering her, and welcome him back into her arms. That ship had really sailed and the writers wrote themselves into a corner if they intended to deliver a neat, satisfying ending. So I was really taken out of a film that I was quite enjoying up to that point.

But while watching I came up with an idea for an ending that I think could of worked:

So the ending proceeds as already written with Pratt going out of the ship to save the day, but before he does, rather than forgiving him and taking him back, Lawrence gives him a kind of subtle nod of respect. Pratt has found redemption for his actions, if not forgiveness. Then while saving the ship, Pratt dies, sacrificing himself.

Lawrence is now herself alone.

Time goes on with Lawrence herself now struggling to pass the time as she leads a life minus human connection. A year or two passes. This can be shown fairly quickly, we've already seen this situation with Pratt earlier so we get the idea. Lawrence is on the verge of suicide when a particular sleep pod catches her eye.

The film ends here. We don't need to see whether she opens it or not, just that she's thinking about it.

This ending I think would bring things to a close more believably while also giving the film more to say, as it explores human nature.