Fate Worse Than Death

A fate worse than death is a consequence judged to be more terrible than dying. Torture is often considered worse than death, as it goes on longer, and so is being allowed to live while all the things you hold dear are removed, killed or spoiled in some way.

Sadly, subjecting Mary Sues to Fates Worse Than Death is simply not practical, as for canon to revert to normal, the Sue must die or be otherwise removed (though this usually involves the Sue dying, for obvious reasons). So the usual solution is to give the Sue a taste of a Fate Worse Than Death, just to teach her a lesson, and then to kill her anyway.