Well, my take on how I'm imagining this situation unfolding going forward is a little different...
A Mod has been on a quiet board forever. He's kept the board clean when issues have come up - which was rare. There's no reason to remove him in this situation.
The stock is being promo'd by groups here or elsewhere and there's an influx of posters who apply to be Mods. If they have a history of being active Mods and/or at the very least (with no previous Mod experience) of adhering to the rules, then likely they'll be added to the board as Mods as well.
As long as the "original" Mod isn't violating the Mod privilege and is actively taking a role in the moderation of the board, then I don't foresee that he would be removed.