It seems pretty clear that Phase Three is going to end with a blow out that will see every single character in the Marvel Cinematic Universe somehow involved. I mean, they're doing a two part Infinity War movie and resolving the storyline of Thanos, whose main motivation in the comics is to kill half the universe (as a tribute to his love, Death). It's going to be the biggest, most cosmic story ever... and Jeremy Renner thinks it will not involve mega-popular Avengers meeting the mega-popular Guardians of the Galaxy.
"We still have to do Avengers 3, 4," he said when asked about a potential Guardians/Avengers crossover. "You’ll be eighty years old by then, and I won’t be Hawkeye anymore. I’ll be Dead Guy."
It's pretty clear that Renner doesn't think Avengers: Infinity War could include more characters (he begins his semi-jokey reply by saying "There's already a lot of people in The Avengers, man!"), but it's also pretty clear he's in for a rude awakening. I can't imagine a world where Marvel Studios doesn't have these two teams share at least one scene together over the course of the likely five hours of Infinity War. The amount of box office they would be leaving behind by not crossing them over is immense.
So why am I running this if I think Renner doesn't know what he's talking about? This is a nice example of why asking actors about movies they have not yet shot is sort of a waste of time. Renner doesn't know what Marvel is doing next, he just knows that he gets a call from his agent saying that Marvel needs him on certain dates. I would be fairly certain Renner doesn't know what's happening in scenes of Civil War that don't feature Hawkeye.
So don't despair. I simply cannot see a future where Marvel does not bring their two big teams together, even if only briefly.