That's kind of the $64,000 question, isn't it?
The only honest answer I can give right now is, I don't know.
Stretching out the hypothetical -- that Malzahn makes Auburn perennially a 9-or-more-win team, and Alabama never wins that game again under Saban, I don't think there are going to be three more titles. I hesitate to speculate on that number, because the playoffs are expanding and Alabama could get in through the back door. But let's just say AU stays at 9 or more and Alabama doesn't win for a long time. That would put Alabama in the same situation Texas is in now, with a successful, older coach in place but a legacy that would be seen as decaying. I think the overall legacy would absolutely be tarnished. If he leaves here with a losing record against Auburn, there's no doubt in my mind it will take some of the shine off.
Therein lies my hope that he'll actually change his approach. If he understands that continued struggles in the UA-AU series could be harmful to the legacy, he'll address it. You just have to hope he's not stubborn enough to dismiss those concerns.