Tossing someone else in as a sacrifice is not a heroic thing to do, full stop. How is it easier to convince yourself that's heroic when it's not in any way than to just let yourself lose the fight as a sacrafice? If you die, there won't be an end game cinematic telling you anything, sacrificing another character is such an anticlimix that it would be moronic to put it into a game (for a less bad example of this, see Oblivion).
If my character dies, I also don't get an end game cinematic telling me that the world has been saved. I just go to the reload screen. I want my game to
end. How have you not got that out of everything I've said so far?
And why are you making such assumptions about what my 'sacrificing another character' suggestion would involve? The sacrifice doesn't have to do all the heroic bits for you. Let's say (and
this is just one example out of a myriad of possible ways the sacrifice story could play out) that the sacrifice has to undergo a specific ritual to prepare and highlight their soul to be the one used to banish Alduin. Now you can undergo that ritual, or you can force some other candidate to do it. Whatever you decide to do, you're still going to have to face Alduin in battle and do whatever climactic thing BGS has planned: the only difference being whether or not your soul gets svcks out of your body.
Hell, the alternative candidates don't even have to be innocent. Let's say that one of them is an evil necromancer. It's hardly evil to sacrifice them now, is it? You'd kill them anyway - this is just two birds with one stone. However, you have to track them down first, wasting valuable time while Alduin is closing in. Do you track them down and force them through the ritual to insure your own life at the risk of Alduin arriving before you're prepared, or do you undergo the ritual yourself to eliminate that risk?
Do you see yet why I'm getting frustrated with these dichotomies? It's hardly a straightforward situation. This possibility would be weaved thoroughly into the MQ so as not to be bland.