First off, any and all contracts are negotiable. People forget this. They think that if a contract is offered, they have to either accept or reject it. Not so. You should always negotiate your contract so that, hopefully, it includes the things you need covered. Always get a lawyer to look over your contract. That way you avoid signing up for something you don't agree to.
Secondly, no editor worth their salt will ask you to rewrite to such an extent that it changes the story completely. For the most part the experience will be very positive, with back and forth between you and the editor, discussing issues as they arise. It will cover grammatical errors, continuity, and, if you have agreed to it, some story development.
My editor for my book Some Strange Scent of Death was professional, accurate, helpful and a lovely person.