If, for some reason, Lebron stays with the Cavs after this season, they will be the favorite in the East for about the next 3 years. That's just about how long Lebron can be Lebron. And then the bottom will drop out.
Lebron has played 41,272 minutes in his career, plus playoffs. If he plays about 2,700 minutes per season (75 games x 36 minutes/game per season), in three years he'll be at roughly 49,400 minutes in his career. For some perspective, Kobe played 48,637 minutes in his career. Only 5 guys in NBA history have topped 50,000 minutes: Abdul Jabbar, Karl Malone, Garnett, Kidd and Hayes. Given Lebron's body type and his playing style, once he goes much above 48,000, he's not going to age gracefully. When he goes, he's probably going to go quick. That's probably going to be about 3 years from now.