It would be great to bring back Quintana, as I think with him and Hill, having a veteran in the rotation is really helpful. I think he's stabilized his value somewhat given that he came back from the injury and pitched solid, but it's likely that the Mets would really like being out of his contract.
From a distance, it seems like their offseason might revolve around Alonso, since either they step up for him and retool slightly, or they focus full-on on retooling the roster and then it's advantageous to get rid of as much salary as possible. I would assume Stearns has a lot of leeway to do whatever he wants, and that situationally it makes sense to tear down.
There's some risk attached to Quintana due to age, so I think that could weigh in his return, but I also figure he's got a decent value given that he has tons of experience and pitching is always extremely scarce. On the other hand, he might be more of a guy that appeals to middle tier or lower teams, since the really top end teams don't want to necessarily anchor themselves to that kind of deal for what might be more like SP4 or 5 and not a playoff starter (if you take the more cynical view of decline -- look at Ryu as an example). All that is to say that I think these factors make it a great play for the Pirates, even if something decent is given up from the depth prospects group. Hard to imagine checking off a badly needed SP with a better contract than 2/26M.