Oh.
Selling them and buying some new servos and drives is likely to be the far easier option, if you do want to change the control.

Lack of program memory on a lathe isn't that big a problem, as most lathe programmes aren't that big anyway.
But it all depends on where you want to spend time and money, between running the existing system, or fitting a new system.

I'd be seeing how much a working Fanuc system is worth, and making a decision from there.