Given a colony stasis ship (ie a ship filled with frozen people to be decanted on reaching the destination), which for some reason cannot reach its destination, how could one (non-frozen) crew-member's sacrifice change that outcome?
Some possibilities:
1) Perhaps there's a debris cloud or solar flare in the way, and if the hero flies a craft ahead of the main ship as an "ablative shield", the main ship should come through undamaged. Strains credibility, though.
2) Perhaps it requires someone to make periodic manual adjustments to something, so needing them to be defrosted often enough that they'll be essentially dead of old age by the time they reach the destination. But what could possibly require adjusting, that the ship couldn't adjust itself, and that could not be tweaked by all passengers, hence spreading the ageing load?
3) Perhaps the ship lacks enough fuel to get the delta-V it needs, but by separating off part of the ship, the ship will become lighter, and so need less delta-V? Strains credibility that this separation could only be done from the discarded part, and that could not be done by the ship's automated systems, robots, etc.
4) Perhaps there's some other non-frozen person who needs to be defeated. This feels unsatisfying because a) then it's not an aspect of the world, it's just a story thing, and b) overcoming other people doesn't inevitably require sacrifice.
5) Infection: if the character is infected they could sacrifice themselves to prevent infecting the rest of the ship, though this is somewhat unsatisfying.
This may still be considered too story-based, or too broad: if either argument is raised, I invite suggestions to resolve them.