Seriously, I was just in a similar situation with a drummer and guitarist who had known each other for that long. I don't know why, exactly, they decided after all that time that they don't like each other anymore, but it broke up a good band with excellent, seasoned players.Those two guys with the 30 year friendship need to work it out. Both sound pretty set in their wants and no matter what happens someone's gonna be unhappy. If I were the OP, I'd be working on a plan B, because this band seems to be heading for continued turmoil and an eventual breakup.
Honestly, in that situation, I think the drummer was just done with dealing with other people's moods and issues, and the other guy was kind of difficult, so I don't really blame him- he'd put up with it for 30 years. When you get to a certain age, it gets like that.
If that drummer in the OPs band is ready to walk, there's really nothing you can do to change it.