I expect him to work on side-projects. As for returning to DT? Unlikely, but if for anything, maybe for a special show or two.
I'm sure A7X will offer him the position, but he'll probably decline, stating his need to spend more time with his family, and that the whole thing with them was only temporary to begin with. Let's face it, he's in his 40's an a family man, the rest of the band are much younger and live a different lifestyle than Mike does/should at this point in his life.
With that, I'm sure Mike will reconvene with Neal Morse at some point in the upcoming year after he finishes his book about his life. Neal has stated that once his book is done, he'll probably start work on his next album, whatever it may be. However, I'm sure Mike will be there to drum, be it another solo album or Transatlantic, or even covers.
And speaking of covers, Mike did say had FIVE albums he had in mind to cover, four of which were done with Dream Theater. Now whether or not he'll reveal the fifth one is up to him, but I'd like to see him form another cover band, covering a full set of songs by that band, as well as whatever album he wanted to cover. He certainly has more than enough connections to do something like that, and I'm sure Paul Gilbert would LOVE to play with Mike again.
And speaking of Paul, what's he up to these days? Perhaps Mike can start his own band with Paul, be it a cover band, or perhaps some new music. Honestly, I wouldn't mind it if Mike and Paul did tons of tribute/cover shows and albums. Mike has always shown he's a music fan above all else, and his prior tributes were all spectacular. Doing such shows would definitely keep him as busy as he'd like, and give him enough variety in playing styles and genres.
-Marc.