The significance of this is that Sansweet is the middle man between the public and Lucasfilm. So to get to Lucasfilm and its higher ups you often have to go through him. He's also been involved with many Lucasfilm projects, from DVDs and the new BD and has written numerous books. He's pretty much a mainstay of the convention circuit as well.
So, it's not exactly huge that he's leaving but it will change fan relation dynamics. He was, after all, the "fan ambassador."