Hiestand leaving was because of complaints/allegations with his coaching style. He was a hard ass and considered "abusive" by two players who transferred, one of whom kept a journal in order to facilitate an immediate PT waiver. That's at least what I heard from a very reliable source. He's not coming back to ND, as unfortunate as that is, unless something has changed on that front that makes him no longer considered a liability. He is by a country mile the best ND OL coach of my lifetime.
With that said, I do not buy that because Eichenberg/Kraemer had an early year with Harry he deserves credit for them while Quinn deserves none. They absolutely sucked early in their careers, and only improved under Quinn. Hainsey is the only guy who played competently from the jump. Banks never saw the field and similarly went from wildly inconsistent -> NFL player under Quinn. Hiestand did not leave Quinn a cupboard loaded with developed talent that he has been coasting on. I know that's not what you're saying, but it's been said/implied by many. The truth is that the worst OL managed by Quinn was during an undefeated season -> they made major improvements the following year -> they were one of the best the next year once he didn't have to deal with Long's scheme.
Fast forward two years from now with healthy Fisher - Spindler - ?? - Chan - Alt and everyone is going to think the OL coach is a genius. But right now, there are a lot of guys playing who just are not ready // may never be ready to play top tier football. Is that partially a coaching issue? Maybe. Is it mainly because there are zero quality players in our senior and junior classes? Certainly. I have a feeling Quinn would look just fine if Banks had elected to stay another year and Fisher hadn't gotten hurt.