This is from the Cover Flap
"Brilliant but troubled Shallan strives along a parallel path. Despite being broken in ways she refuses to acknowledge, she bears a terrible burden: to somehow prevent the return of the legendary Voidbringers and their civilization-ending Desolation. The secrets she needs can be found at the Shattered Plains, but even arriving there proves more difficult than she imagined."
I don't know that this implies that Jasnah is truly dead, but something happens where the responsibility of preventing the return of the Voidbringers, and finding the path to Urithiru becomes hers (Shallan's). Could they have gotten separated? Possibly, but why would Jasnah not make it to the shattered plains if she has the transportation surge? It's obvious something goes wrong, and Jasnah, and Shallan are no longer travelling together to the Shattered Plains. Hopefully nothing serious happened to Jasnah.