I think, the only way that LeBron comes back to Cleveland is if they manage to lure another big name star there. The team just isn't good enough as it stands right now to compete for a title, and I think that, more than anything, is what will likely cause James to defect to another team.
This is the one thing I don't understand about the League. They talk about teams getting themselves cap space for the 2010 offseason to lure away LeBron, but what many of them have neglected is that the Cavs have quietly put themselves in a great position to lure another star to Cleveland. They are the only team in the League, currently, who will be in the position in 2010 to sign two elite players (albeit because LeBron plays for them) which means they are the only team who could put, for example, LeBron and Bosh together. Cleveland might not be a big market city, but anyone playing for them and competing for a Championship has the opportunity to get God-like status from the fans, given that the city has gone so long, with so many major-sports teams, without a Championship.