Well Nightmare Cinema was never really a 'band", so I don't think it would have to have Sherinian for it to make sense. It was just a fun thing they'd do sometimes.
As much as I would love it I just can't see MP ever rejoining DT, unless it's for a one off event in NYC, like a charity event per se.
Especially considering Labrie, and how Mangini is just the drummer now, it just doesn't seem in the cards, and we're all over it, right?
Unless Mangini wanted to retire and teach full time again?
So... I could imagine MP pitching an idea to reunite in a sort of typically MP tongue-in-cheek sort of way, as Nightmare Cinema, the closest thing to a DT reunion.
Also I am like joking .... but come on, it would be hilarious, AND awesome.
And god no, I am not suggesting Portnoy on Bass, Petrucci on Drums etc... just the name would be the "joke", a REFERENCE to DT, but a full real album, tour, etc. Fun.
Or it could just play out as a whole new project, no DT references at all, but with the 4 of them.
Imagine a fully instrumental "DT" album. 80 minutes of "Stream of Consciousness".
A more likely scenario over him actually ever rejoining. IMO