LeBron will leave Miami because it is really time for a change for him anyway. He should join a new team, make a new start, and rake in more cash. They can give the starring role on the Miami Heat team to someone else. There are so many trades and new contracts in basketball that things like this are just expected.
LaBron James is still looking to play somewhere where he can be the cornerstone of a long-term dynasty. With his two running mates looking for greener pastures, it's only a matter of time until he starts looking at those same pastures. I think the challenge of taking another time to the top will get him to make the move.
Lebron James has had a great history with the heat, but the time has come to put his talents to use elsewhere, and this will be good for James as well as the Heat. With the salary necessary to keep Lebron the heat could put a seal on other top notch players like Carmelo Anthony, as well as spend some money on new talent. In the meantime Lebron James has a great offer from his home team, so to speak, the Cavaliers. He would be great asset to them, and by joining would give both teams a chance to improve.
It is my belief that Lebron James will not stay in Miami in the near future. It is common for basketball players to move to different teams when the opportunity comes up. Lebron James is a free agent, and so is capable of leaving Miami if he wants to. Given Miami's record, it would be beneficial for him to leave the team.