Dream Theater has proven that they will thrive even without Mike Portnoy. I have listened to ADTOE at least once every day since its release. It's been long enough that I have no reason to believe that my love of this album is primarily influenced by its newness. Instead, it truly is, for me, one of their best.
Mike Mangini is incredible to hear and watch. As far as drumming goes, I perceive no void. Moreover, MM's finesse is a welcome addition to DT's sound.
What about the non-drumming aspects, though, that MP brought, such as customization of setlists and the glorious Ytse Jam releases? Does this all go away with him?