Jeska had already lived several lives: barbarian, cursed destroyer, false god and planeswalker. During the rift crisis, Leshrac tried to steer her power toward his own ends. By the time his schemes were exposed, the remaining wound over Otaria still threatened everything, and ordinary force offered no answer.
Radha, an elf whose heritage made her unusually attuned to Dominaria's mana, became the focus through which the repair could be directed. Jeska channelled the necessary power through that connection. The act closed the last great rift, but Jeska did not survive it.
Her death completed the physical work of the Mending. It also underlined the event's central idea: reality was not restored by planeswalkers proving they were above everyone else. It was restored when they accepted limits, answered for the damage around them and spent powers they would never regain.