The lines from the last few sentence in Avengers:Age of Ultron, when he tells Steve Rogers that, “We must take a leaf out of Barton's book and Only an Avengers can use my phone shirt.” He might return that way with Pepper that way or maybe We might be unfortunate to see him sacrificing his life, which is a little unlikely as he was the face of MCU and carried the Avengers on his shoulders and he kickstarted the MCU with Iron Man. 
