Ok, so as some of you may be aware from Avengers: Age of Ultron, Quicksilver (unfortunately) dies. Yes, the beloved and witty youngster dies. As in is dead, a corpse, a cadaver even! Alas! I have a theory! As less of you might know, two infinite gems remain to be seen in the Marvel Cinematic Universe (Soul and Time, the former of which is likely to be in Dr. Strange). My theory, is that somewhere, somehow, in Civil War or some other MCU movie the time gem will be revealed! Yes. The time gem. Not soul, but time.
Now, some of you are wondering "Why time and not soul?" Simply put, Dr. Strange, as of now, is nowhere to be seen and he has the only logical connection to the soul gem. "How" you ask? Well, that's where my theory kicks in!
My theory, (as flimsy as it may be), is that once the time gem is unveiled to those who would revive the lovely bugger, they'll set about seeking a course of action! (Most likely Scarlet Witch since, you know, sibling love and all that). On to the actual theory of Quicksilver's reanimation! My theory about the time stone is that Scarlet With (or someone else maybe) uses it to reverse Quicksilver's personal physical clock! They turn back Quicksilver's clock and basically rewind his death like the end of a good VHS (people still know what those are, right?) Because these are movies and Vision could explain it much better.