I took the question to mean if DT broke up, which current progressive metal band (for our circles, not the crossovers/modern/etc) would become the biggest in the world & carry on the progressive metal legacy as we define it? To me, that means the band is universally beloved because of their consistent track record of high quality progressive metal releases. It has nothing to do with who is the most "progressive" or "releasing different album" every time for the sake of being progressive.
Pain of Salvation were the undisputed heirs in my mind until Scarsick. Now, one album does not make the shark jump. However, they followed it up with albums that were even more alienating to the not just the casual PoS fans, but the fans that had been with them since the start. Yes, there will always be diehards that will support them and love every release because they connect with the band. However, that is irrelevant to the question being asked.