Lebron...oh do I look forward to not hearing the hoops media utter that name every 30 seconds...
On his longevity: he seems to have expressed (by returning to Cleveland with younger stars in KI and KLove) a desire to have other, younger stars sort of prop him up and carry him along at least for some stretches (my interpretation there), but in his play, he is always the center of the action and carrying the load.
The questions on his longevity are whether he can be a second or third banana, and eventually role player. (My guess is no).
If he wanted to, barring serious health issue, he could be a stretch 4 until he's 40 and be a 15/10/5 guy in 30 minutes.