Like you said, the money was never mentioned again. What we do know is that Chandler smokes again still in S3e17 The One with the Ski Trip, so its extremely likely he didn’t end up with the money, perhaps giving it back to Phoebe or donating it:
Phoebe: Chandler, what are you doing?
Chandler: (Pointing at his smoke) Oh, my god!
Joey: You’re smoking ...
Because Friends ran its course.
The story was completed: Ross and Rachel ended up together, Monica and Chandler have children, Phoebe and her boyfriend were planning to follow up and Joey was moving to Hollywood. There was nothing more to say, the group of young, carefree friends was no more - they were now in their 30s with own families.
The out of ...