From the Mormons I knew, if he came out as gay he would be disowned.
He's gotta "stay" so that he can get married and procreate. There are "spirit babies" who are currently in heaven waiting to come to Earth to fulfill Gods plan.
He's gotta "stay" because if he doesn't obey the Mormon God, he cannot become a God himself and rule over his own planet in the afterlife.
He's gotta "stay" so he can pay tithing (10% of his income).
He's gotta "stay" so he can become a missionary and convert others.