I'm not assuming anything (except that Pyne won't make the NFL). You're the one who seems to be assuming that both Pyne and Buchner would transfer if we brought in a 5Y.
I said I could see Pyne leaving, going to some G5 or low P5 where he could start, but could also see him staying and finishing his career at Notre Dame where he is (currently) proving his ability as a solid backup QB. Depends on what he wants.
As for Buchner, if they bring in a transfer who is obviously better than him and anoint that guy the starter, yeah maybe he moves on. But I think Buchner should, and will, get a fair shot to compete for the job. If a transfer's not OK with competing for a job, maybe he's not the guy we want. (I'm also not sure trading potentially three years of Buchner for a one year grad transfer is a wise move, though that probably depends on how good the grad transfer is, and when Carr shows up.)