I've just had a snoop through Clark Gregg's twitter, and his latest tweet confirms he is signed on for more marvel movies, here is what was asked by a follower and his reply to it:
SPOILER WARNING:
Well regarding to the previous spoilers stating that Agent Coulson dies in The Avengers, even though the leaked script is an early version of the final script, I don't think he will... Unless he's a Skrull of course, which noone would know about other than us, oh the irony... God, why did I have to read those spoilers?
My first article ;)