It's always a pleasure to read what Marvel's movie kingpin has to say, regardless of the topic, and Joss Whedon's recent interview with EW was no exception. He covered a variety of topics; among them, the roles villains play in the Avengers movies, and the possibility of portraying the death of an Avenger on screen.
In regards to the villains in the Marvel Cinematic Universe, Whedon doesn't plan on re-using any in the Avenger films.
Every movie is going to be a different villain. Loki's awesome, and he is awesome in 'Thor 2,' but 'The Avengers' is a different thing.
So, as great as Loki was in The Avengers, we won't be seeing him in the sequels, even if his brother will be joining up with the super group. It seems, with Ultron as the next villain, that we may be getting a different theme for the enemy of each movie; Loki represented the "God" aspect of the Marvel Universe, and Ultron will be show casing more of the scientific/engineering side of the series.
On that note, with such an unstoppable enemy in the form of Ultron on the horizon, it makes one wonder; will one of our heroes die in the fight to save the world? Well, according to Whedon, it's a possibility, but it doesn't seem likely.
Um... maybe? But I'd have to have a really good reason, a really great sequence for [Marvel executives] to go, 'We'll cut off a potential franchise, that's fine!' They know, as any good studio does, that without some stakes, some real danger, how involved can we get? We don't just rule it out across the board, but neither is the mission statement 'Who can we kill?' We try to build the story organically and go, 'How hard can we make it on these people?'
This makes a lot of sense, and I never thought about it in terms of the fact that they wouldn't just be ending the character's story, but also, most likely, the possibility of that character's franchise continuing (except for maybe through prequels and such). Is this something you'd like to see; a major character dying for the sake of the story?