i disagree with Juvia`s, Gray`s and Mira`s part in this theory, but whatever...
and Zeref dying and Natsu not? it seems a bit impossible to me... Zeref said so himself, when he will die, Natsu will also die, because of that Natsu is a demon from the books of Zeref.
i think that those characters will die :
Makarov - more some times he have to be almost die? i want him to die already.
Zeref - Natsu will kill him
Natsu - will die as result of Zeref`s death
Jellal - will die when he protects Erza from someone from spriggan 12
and about Wendy and the rest... i dont think that they will stay at this timeline after the war is done, im pretty sure that somewhen Lucy will close the eclipse gate for them, so they`ll return to their own timeline, before 400 years. also for learning more about themselves, im really looking foreword for this.