Miami had a very successful run (2 championships) but Dwayne Wade is clearly not the player he once was and Bosh seems to have lost the star power he had in his Toronto days. LeBron would be smart to leave, join another team and try to get another ring, Cleveland has got some fantastic talent (Kyrie is a superstar, IMO) and young prospects
As for Carmelo, I think he becomes a Laker, he's going to get the money and the chance to play with Kobe. They won't win a title next season even with Melo because they lack the "glue" guys and tertiary scorers but it would help prolong Laker success for the next couple years