I personally will be pissed if Portnoy comes back. I wanna see and hear what this band is capable of without Portnoy.
Also, some food for thought:
The first time Dream Theater experienced significant turmoil and felt the need to establish or "prove" themselves, they created Images and Words. The second time that happened, they created "Scenes From a Memory". This is now the 3rd time. I am as much of a wayward fan of the post-Scenes stuff as anyone, but I do legitimately think this could lead to them unleashing their next GREAT album.