Here what I think.

I think dex is gonna almost die in flashback because

1 hasn't almost died since the first book
2 I most likely will happen trying to save biana

Or maybe keefe cause

1 hasnt died since book 2
2 might die from broken mind I think this because of the description of the book synopsis
3 might die from saving sophie or fitz

Remember no one is really gonna die

hopefully...

EDIT:

Hahahahaha I was so wrong.
Welllllllll Keefe got hurt emotionally but im still wrong.