I haven't heard him talk about a 50th fight. This is his last fight, definitely. After signing off his contract with the Berto fight, if the TV people wanted to get him back in the ring they would have to offer him Crazy money. And if they offer him crazy money, they will insist on him taking on an epic challenge.
At Floyd's age, he doesn't want it anymore, and who can blame him.
The only possible way we'll see Floyd back in a ring is if he spends everything, which is virtually impossible. Also, that would take years to do and he would be too old, it would be too late.
This is the real world, it ain't no Rocky movie.