If they remove the Lae'zel and Mindflayer romance and maybe even Shadowheart or Halsin with M!Tav, I will be totally okay with Spawn rejecting this Mindflayer romance too.
And no, I'm not saying that the Elfsong Tavern scene should be changed! It's perfect already, but it still, IMO, leaves the possibility open for Spawn to get back together with M!Tav. He says so himself: "Maybe we will adjust, maybe we won't, but you still mean too much to me to just walk away". After this it can make sense he has adjusted after 6 months period.
Yep. Wyll does that in his Duke route, IIRC, because people can't see their Duke with a mindflayer. Still together with M!Tav romantically, though.