Like others have said, I thought this HAD to be a joke when I first saw it on Facebook. Mangini seemed like the ultimate team player and the other guys appeared to really adore having him in the band. His being (evidently) replaced is something I *never* saw coming and I must admit to feeling bad for him even if I've always preferred MP's drumming.
This feels so sudden it's hard NOT to want to read between the lines to understand how it happened. I'm guessing it was initiated by JP after the great time he had touring with MP again last year. And this quote says a lot to me - "I know that his return will bring a renewed spirit, passion and energy into DT that all of us, including our fans, will joyfully welcome." Although loving having MM as a member all these years, it sounds like even he felt that some spark was missing when it came to planning the next step. The less than fantastic attendance for Dreamsonic probably factored into this as well.
As far as future performances go, I'd like to hear them still play a few MM tunes just to hear MP's take on them. I can't imagine them NOT playing The Alien again as it obviously has special significance. My biggest wish is to hear The Glass Prison live or even better, the entire 12 step suite which was never performed as one piece by DT!
It's going to be fascinating to see how this all unfolds over the next year!