To those of you calling this selfish:
You're completely ignoring that the ritual murder is still on the table.
You're the shortsighted selfish ones, in the worst case scenario of this ending, where they fail to find any other solutions/have children with her powers, she can still die by his hand at an old age, both freeing the last batch of people and having prolonged the lives of thousands of people over her life. (The last batch being possibly much larger too, if she managed to train her powers.)