Zimmerman will be the backup. I believe SFI has already hinted at this. Zimmerman just needs a little time to get into the system, which he will continue to do this spring and summer. I have no doubt he will be the #2 this fall, and will (effectively) bridge the gap between Studs and Boltmann.
Heidelbaugh sounds like a good athlete, but has a slow release, and granted his one career pass was a TD, but I don't think it gets any uglier than that. That TD was 100% credit to Wanzek.
Bolinske also sounds like a decent athlete, but I do not see him being the #2. If he is, that is due to the coaches lack of success in finding quality depth, or Bolinske stepping up far beyond his HS recruiting projections.