Pixar and Disney had a contract to make 5 movies. The Incredibles is the fourth and The Cars is the fifth. It takes at least 3-4 years to make one of those movies from start to finish.
My understanding is that Disney owns all the rights to these first 5 Pixar movies, so if there are sequels to any of them Disney will make it. I hope Disney doesn't shy away from promoting the Pixar characters in the parks. I'm still waiting for the Monsters Inc door ride, and I would love to see rides or character breakfasts with some of the other Pixar characters.