Is rey mysterio going to be world heavyweight champion again?

No Rey Mysterio Jr. is not Rey Mysterio. Rey Mysterio is the one who trained rey mysterio Jr. Rey Mysterio is rey myserio Jr.'s uncle

You are partly right in that Rey Mysterio, Sr. did train Rey Mysterio, Jr. BUT Rey Mysterio, Jr. has dropped the Jr. off of his name is known as Rey Mysterio. So in that regard you are wrong.