Did the heroes who disappeared in Avengers: Infinity War die? Will they return?
IMHO I think that all who died before Thanos snapped his finger (Loki and Company) will remain dead, but those who were turned of ash after the snap are predestined to return.
"Predestined?" you ask. Yup!
In A:IW, Doctor Strange said he saw 14,000,605 versions of the future, and tells Stark that in only one of those timelines did the Avengers end up winning. From that point on, everything was hinged on the one outcome that was needed by the Avengers, and that Doctor Strange and Spider-Man - as well as the others who were not on Titan at the time - being turned to dust was part of the program to ultimately win.
Guess we'll have to wait until May of next year to prove if I'm right.