Stupid question, or is it...
Can a band such as Dream Theater be a legally defined entity, independent of whoever happens to be playing in the band at the time? Is there any reason that when JP and JM retire from the band that they can't be replaced, leaving DT with no original members, but they still write, record, tour, and play a mix of new and old material?
When MP left he may have been thought irreplaceable, but he wasn't.
Some bands are defined by a constant line-up throughout their full existence. Rush (except for the first album) and Queen spring to mind. Others change personnel every record. DT are somewhere in between, with if my counting is correct, 9 members so far on the records, so roughly one replacement every 3 or 4 records, or on average every 7 years. Could this continue for ever, with new people coming in whenever one leaves, such that we'll have a Dream Theater as a living entity in 2067?