...by some miracle defeated Gray Boo and ate him as a cookie or some sheeeeet. Would he have gone back to his previous power and have anger-management problems like before or would he have stayed the same?
He'll be return as Fat Boo in terms of power but I don't know personality wise. Even though Good Boo is no longer connected to Pure Boo (since Vegeta cut the pod between them) yet he managed stopped him from attacking Mr. Satan.
He remains the same. Gotenks comes to fight him. After a series of gag scenes in the fight, Buu and Gotenks become friends. Everything is fixed with dragonballs and Goku stays dead. If Beerus wakes up, he destroys the Earth after Buu has angered him, since there are not enough Saiyans to produce a Super Saiyan God. If Beerus doesn't wake up, Golden Freeza destroys Earth.