Barring Athlead going under, there's no good reason for Jim to not end up in Philadelphia full time. I feel like the story of Pam getting the opportunity to paint the mural was introduced because the writers wanted to make it look like there was some reason to stay in Scranton.
I think Pam confides in Dwight about not wanting to move to Philly and that she can't do it or something, and Dwight convinces Jim to stay by warning him that he will lose Pam if he goes.
But probably not. I have no idea what they are gong to do.