I think a better way of putting it is that Kobe is also threatening to go play in Europe.
First, neither he nor LeBron have been offered anything and $50 million for a cameo one year appearance is ridiculous. I can't see how a Euro team could ever make that money back.
Second, I don't see either going for a myriad of reasons.
The elite players in the league can threaten Europe all they want in hopes of the NBA changing the CBA and the maximum earning of a contract but until 5-10 of those elite players are lost for a significant amount of time, nothing is going to happen. Stern will simply say to go have a nice one or two year vacation and when you want to cement your legacy as one of the best ever, the NBA will gladly allow you back to play.