Yep. I am actually off and on working on a fantasy story based on an old RP. That partner passed recently (I got permission to use some of our RPs long before then, since her health was declining and she couldn't play anymore), but there's lot of good stuff to pull from.

I also had other partners influence some of my OCs and original worlds. I have characters who would not be the way they are today without my partners. Even my current (albeit fandom-based) RPs have given me ideas to toy around with.