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Part of The Time Traveler's Dilemma - in many cases if they succeed, their story becomes The Story That Never Was, erasing themselves and all they did to save the past.
If the character is acting on information about the future that they know due to time travel, it's a form of them claiming Omniscient Morality License.
Edited by BattleMaster
Expendable Alternate Universe alludes to this in its fourth paragraph.
Great suggestions all around! They led me to Reset Button Suicide Mission, which is pretty spot-on on the heroic side, but I'd love a "Reset Button Colateral" for when the sacrifice is not limited to the person calling the shot.
If by collateral you mean the issue that positive things can have happened that altering the timeline would erase, that part is The Time Traveler's Dilemma one I linked. (For instance, the classic "Alice and Bob have a daughter Charlie in the Bad Future who will likely be erased if they undo the event that drove them together.")
Reset-Button Suicide Mission is a good find for the part where the reset button can negate many of the costs you paid to push it, though; I'm adding a mention on TTD about the overlap between the two because they're so closely tied to one another.
Edited by Scorpion451
The time traveler is willing to sacrifice anything on his quest to change the past, since no such sacrifice will persist.
Is there such a trope? Should there be one?
Edited by Xhosant