I had the chance to hear Pete Docter (directer of Monster's Inc)speak about a month back.
Someone at the lecture asked if Pixar had plans of leaving the relationship. Pete said that there was no plans to split. I do know that the deal that Pixar had with disney was for five movies. It is also too bad that Disney got rid of its Feature Film Division (3D department), because there was alot of talented people there. I guess the greed of Disney finally caught up. The times of animation has changed, people want to see films that apply to children and also adults at the same time. Pixar has found the mix, tell a story and leave of the singing characters. In the first Toy Store film Disney wanted the character to sing Pixar said no. The rest is history