There was a long discussion with me, Ian and a few others about this specific plan in the Bills post-game thread a couple days ago. Basically my plan is the same - sign Garoppolo for a few years, trade Mac for a 2nd + 3rd (he'll fetch that, I'm pretty sure), use those picks to invest in the OL, and develop Zappe while Garoppolo starts for the rest of Zappe's contract. If you don't feel like Zappe is the guy by the end of 2024 then extend Garoppolo a few more years and draft another QB before Zappe's deal runs out at the end of 2025. Garoppolo will get hurt, yes, but Zappe can manage games in his absence.
And yeah all of the above is predicated on the assumption the coaching gets fixed.