And then Dave Mustaine gets sober (good for him, legitimately) and somehow loses his mind AFTER getting clean leading to him becoming a right wing religious nutjob.
Without knowing anything about the dude, that seems very plausible actually. If he used to be an alcoholic and/or substance abuser, that is almost always connected to some sort of emotional trauma, with the substance being used in an attempt to deal / cope with it.
If someone like that then turns fully sober without having worked through their issues, they will just find something else to be excessive with, like religion, especially if it played a role in their getting sober. Unhealthy behaviors don’t disappear like that, they just transfer to another outlet