My guess is that the game plan is pretty simple and they’ll run roughly the same template regardless of who is starting. It would benefit Mac to run something simpler for his own protection his first week back, especially against a defense that’s very weak against the run anyway. And if you have a choice between two QBs, it makes a lot more sense to go with the much more experienced, more talented guy who knows your system better, even if he’s a little limited by an injury. I’m sure Mac is capable of executing a run heavy game plan, and would probably be able to make some calls at the line that Zappe can’t.