Re: Enlarging a P-90 route for a Humbucker?
Judging by your skill in removing a nut, I would definitely NOT recommend that you do the rout job yourself.
However, that neck can still be salvaged. It's still possible to remove the remains of that nut and replace it with a good one. It will end up half Gibson style and half Fender style unless you want to put a lot of work or money into it.