In the present, as long as he's employed by ESPN it does nothing. He'll still be the top story on every Sports Center and he'll be on their webpage every second of every day.
In the future, it tarnishes his legacy quite a bit. A day will come when LeBron isn't the "hot story" he is right now. Other players will take his place as he ages. And, in a decade or two, when people look back on his playing career, they'll see a championship (maybe two), but they'll also see one Finals loss, two Finals loss, three Finals loss...
This is all dependent on the Spurs winning this year's Finals, but... Duncan will be 5-0 in the Finals. Even if they lose, he's 4-1.
We all know Jordan is 6-0.
Kobe is 5-2.
Bird is only 3-2. Magic is only 5-4.
The point is that they ALL have winning records. So, it's not so much that LeBron will have lost a Finals or two, it's that he'll potentially have a losing record in the Finals. That tarnishes a legacy quite a bit.