This very rare 1-on-1-on-1 MMA fight would indeed be unprecedented. Almost all techniques in MMA assume a single opponent and I don't think we really know very well what works in a three-way fight. Game theory suggests that the weakest two take down the strongest, which in terms of skill is Zuck, but in terms of size is Musk. Though CSW has questionable logic skills, both Musk and Zuck will try to convince CSW to join them in ousting the other guy. Or it's possible that they know he's scum and won't fight fair, to get him out first. Who knows?

I suspect that this is something like a game theory three-body problem.