I'm more inclined to believe that each turn of the wheel could be different, but might not be. My recollection of Roland's last reaction is that he recognizes what is happening (indeed, has been happening over and over again) only as it is just a moment too late. This might indicate that he knows in that singular "out-of-time" moment in the doorway exactly what comes next, or it might not. I've only read the thrilling conclusion (the last two volumes) once, and I would have to look at it again to be sure, but what I believe -- based on what I remember -- is that Roland may be able to retain certain knowledge from his journeys, but he does not retain the knowledge that he's trapped . . . and hence is having trouble learning how to free himself from his obsession.
Roland's realization isn't that he must do it all over again, but rather that the quest isn't over for him. His memories fade out of kindness, not as part of the punishment. The show must go on. It will not be Jake he finds at the way station this time. It will not be Eddie Dean that he pulls and through and whose soul by the quest saves. More to the point, it isn't Roland's obsession that is trapping him, at least not exactly. Consider where Roland restarts. It isn't in his wild youth. There were many mistakes there too (but of a different kind). His obsession began long before he followed the man in black across the desert. Roland is a being who has done many things which have caused himself and others pain. Why the desert? Why is it exactly at that point where he returns?
I would point out that the the many painful mistake and experiences that Roland endures prior to the desert do not repeat because he was still "standing and was true" while engaging in them. Sometimes bad things happen to good people. Sometimes the good guys still suffer when they do the right things. In fact, doing the right thing leads to more suffering than not. The reason Roland doesn't restart begin his journey the Tower all over again from Jericho Hill or by the clean sea (or any point of your choosing prior) is because it is with Jake under the mountain where he did NOT stand and be true. It is there that he let his obsession take precedence over the will of the white. Prior to that (at least in what we can see) Roland does many dark and painful things, but he did them all by the code and with intentions that were pure. I would argue that saving the Tower and redemption did allow Roland to take a step toward ending his quest (however that will fall out), but that he was doomed to go around the wheel again the moment he chose to let Jake fall. Roland knew it himself, just as King knew it too.
We must glean from this (and what the Man in Black says) that Roland has continued his quest on the wheel of Ka many times. What we don't know is if he always restarts in the desert. Think of it as a Ground Hog Day (the film), like experience. Perhaps Roland is always going to restart his next turn of the wheel just before the point where he failed. With this dreadful knowledge, we can speculate that Roland's previous turns of the wheel likely involved many other people who were chosen by the Tower, dealt if you will. I expect that each time in the past, when Roland failed to stand and be true but still reached the Tower the wheel turned over, and a new set of people would be drawn into his life. It would not be the same people because their needs have already been met. Do you see where I'm going with this? It would also not be the same story because time in the keystone world only moves in one direction. That part of the Roland's tale, where the Tower is saved in the keystone world, is set and immutable. What will he save next time? That is the big question I suppose, but it would be something different, just as I expect his companions will be different too.
We must also accept that we may never know the answer to these questions. While I suspect King will live a long, long life and be writing books until the day he suddenly wakes up in the clearing at the end of the path regretting he didn't get to finish just "one more"... he might choose to not answer these questions. Roland's quest is an end in and of itself. We take solace from the fact he is out there and that he might one day know peace, but we know that the Tower and all the levels of reality it upholds needs Knights, or Gunslingers if you prefer, to sustain it and thus us.