Possible spoilers may follow, proceed with caution...
[The Avengers: Age Of Ultron](movie:293035) has long been looked at as the end of the Avengers as we know them. A good idea of where things will end up for these characters can possibly best be described in writer and director Joss Whedon's own words. When he was asked about the Avengers sequel he gave this nice little quote...
"My instinct was, 'Let's just come out of the gate saying there is an Avengers.' So we can have more time to pick at them and tear them apart and hurt them and ultimately destroy them."
So yeah, when all is said and done in Avengers 2, we're probably not going to see the team hanging out at Tony's favorite shawarma joint enjoying a nice lunch together. The team will be destroyed and if the events of Captain America 3 intend to even casually follow the events of the Civil War storyline from the Marvel comics, they aren't going to be repaired any time soon.
This is where the life and death of Mr. Captain America, Steve Rogers, hangs in the balance. We know that [Captain America: Civil War](movie:994409) won't be a direct adaptation of the comic book - there's just too much in there to bring to the screen and the MCU has its own version of things going on. But there could be a good reason that they picked Civil War to begin with - the series ends with the death of Captain America.
Captain America's Fallen Soldier
On top of that, they also chose to introduce two key figures in this scenario in the last Captain America movie: 1) The Winter Soldier aka Bucky Barnes aka the one who could conceivably carry the Captain America torch and 2) Sharon Carter aka the one who pulls the trigger on Steve Rogers.
A lot can also be deduced from the contracts that the actors playing these characters are under. Most of the main Avengers cast signed up for six movies, a number that is coming up for most of the actors after Captain America: Civil War. Considering the fact that only Thor and Captain America have movies lined up in Phase 3 of Marvel's MCU and it'll be four years until the next Avengers movie - there are plenty of reasons to think that we may have some superhero deaths on our hands in Captain America 3 and Thor 3.
Just as there may be a good reason Captain America is going with Civil War for its next installment, there could be a good reason Thor 3 is going with Ragnarok. The Ragnarok, or Asgard apocalypse, is something that has occurred in the Marvel comics more than once. But if there is one way to kill a God, not an easy thing to do mind you, it is to banish him to earth. This is one way to prevent an Asgardian from dying during the Ragnarok, but it is also a way to make your God a mortal.
Of course, no Marvel character stays dead for long but it is a little curious that both Thor and Captain America have died in the comic books not that long ago, however temporarily it may have been. Both characters have reemerged from death in a different version (with Bucky Barnes taking over Captain America duties) and this might be exactly what the MCU has in store for these guys as well.
Oh, if only Hollywood could come up with a way for actors not to age. Ok, I'm sure all the plastic surgeons in Los Angeles will testify that it's not like they haven't been working as hard as they can to slow down the process, but it is a shame that the MCU doesn't have the benefit of the comic books ability to keep their characters relatively the same age forever. The sad fact of the matter is that these characters will either see their deaths become an integral part Phase 3 in [Captain America: Civil War](movie:994409) and [Thor: Ragnarok](movie:956858) or they'll find a way to bow out gracefully and pass the torch, or shield, or Mjolnir, or whatever the case may be.