Except the end of the season isn't the same as the start of the season.
We all know how it goes with Lebron teams. They'll look great, then at some point in mid December they'll lose two games in a row, and the media will start asking questions. First time AD sees a news report that asks ''Does Lebron Have Enough Help?!'' will be a wake up call for him.
If he has to go through months of that, and then they don't even get homecourt in the playoffs (or possibly even miss the playoffs, which isn't out of the question depending on roster health) then who's to say he decides to re-up there? He already spent the summer talking about how he'd love to play in Chicago one day. Maybe home will look a little brighter to him.
I'm not saying that will happen, I'm just saying that there's no guarantee that now he's in LA, he will want to stay there. The grass is always greener until it isn't.