Sacrificing self might be a nice game-ending in a single player game, and a refreshing change from the "lived happily ever-after" classic.
In a multiplayer, online game, a player might get such great advantages from joining an organisation/guild that depends on the fame of its death-defying members (like the Sardaukar, or the Ninja), that he would rather die than lose this advantages. Such organisation might also decide to execute members for cowardness, so, when the time comes, you have to choose betwen a cowardly flight to an uncertain and humiliating future and a probable heroic death. Now, if there are at least some 5-10% chances of survival, and great rewards waiting if the player beats the odds and lives, the right choice might not be so hard to make. Also, the members of such an organisation know that any cowardness harms their hard earned power, so a player might begin hating and despising and punishing the yellows. If he finds himself in a must-sacrifice position, he''ll know what to do. And if a player has survived sometimes because of other team players sacrificing (or just risking their lives) for him, he would really have to be a lame looser to decide that his virtual life is worth too much and flee. The irony is that each member of a team made of ready to risk death players might in a lot of situations have a better chance of survival than a wanting to live team.
The most difficult problem here is creating enough situations where a player has to choose betwen his team and himself.
Oh, and of course lengthy time eating killing 11000 monsters for XP is out of the question if such an approach would be taken. But if the character building is mostly a reward for taking risks, the player may even want to face nearly certain death, for a quick boost to his character. Game Rituals where in the presence of large croud of members the courageous get promoted, their acts of valor recalled would also help.

I''ve been meaning to say this ever since this thread was born.

IIRC, you''re a B5 fan. Remember what happened with Sheridan when he tried to sacrifice himself? (Both times?)

Alternatively, you could implement a Ransom feature, where your crew and yourself sacrifice the ship (ram, self-destruct, etc.) and escape in Pods. A percentage of you (dependant on skill & tech levels) are caught, and have to pay a ransom to get back.

Obviously, if you can''t pay, you''re screwed. If you only have enough for some of the crew, you have to make a choice, and that will influence future opinions about you. And if you decide you can''t be bothered forking out for your crew, you risk having no one want to work for you in the future.