He wont leave the Heat. I imagine once Wades knees get the better of him, and Bosh is traded, LBJ will TRY to get players like Melo, Wall, or a Favors/Cousins player. I know some of those players are RFAs, but lets be honest, LBJ has the power of persuasion on his side with now 2 titles and maybe more.
So I imagine Riley will attempt to retool the heat around LBJ