I have some theories on what's going to happen in the Marvel Cinematic Universe, based on other theories and comics I've read, and the trailers that have been released. Granted, trailers are often misleading, but who knows? It's fun to speculate.
In The Avengers: Age of Ultron, I believe that Thor is going to die. In the trailer, Thor's hand can be seen next to Captain America's shield. It looks like Thor is either unconscious, or dead. Some may argue, "Wait! Thor 3: Ragnarok is coming out next year! How can Thor be dead?" Have you read up on Ragnarok in the Comics? Ragnarok is not only an event that destroys Asgard in Norse mythology, but also a character in the Marvel Universe. During the Civil War storyline, Reed Richards introduces his creation to the world. Ragnarok is a cyborg clone of Thor. He was created in the comics after the (short term) death of Thor. If Thor were to die in Avengers, Tony could easily create Ragnarok. This would keep Chris Hemsworth in the role for at least another movie. As for the actual event of Ragnarok, I don't know what to expect.
I also think Captain America is done for. Either at the End of Captain America: Civil War or Avengers: Infinity War, he's going to die. In the comics, he is killed by Crossbones (one of the confirmed villains for Civil War) and Thanos (the villain of Infinity Wars). I think it is a safe assumption to make that his end is nigh. Especially as Chris Evans' contract runs out. Additionally, this will leave a space for Bucky to take over as Captain America, and Sebastian Stan still has a lot of movies left in his contract. I am personally excited to see how Bucky as Captain America is portrayed in the Marvel Cinematic Universe.
What do you think? Do I make any good points? Or am I just having too much fun speculating?