Pretty strange that he could simply rescind his guilty plea after all this time--he should have been sentenced already.
When you go to court, talk to the prosecutor and have him or her explain exactly what is going on. You have a right to know that.
I don't know what will happen in court, because I don't know what kind of proceeding is scheduled. Just try to get a good night's sleep and you will find out tomorrow what is going on.
Good luck, I'm sure you will be fine.