You’re obviously a strong and capable student. As others have said, the “outcome parity” path of getting to a DO program from UMich is not insurmountably steep.
In my opinion, you should choose the program you are really drawn to, not back into something out of fear. If you genuinely like Nova and the BS/DO program, that’s great! But if you would really love to go to UMich, and you’re just worried about having fewer guarantees… well, a career as a doctor requires confidence, so if that’s your goal, you might as well lead with confidence and trust yourself to succeed at a challenging school. If for whatever reason you don’t end up going to med school, the opportunities at UMich are vast.
Truly, if you were excited about Nova, I wouldn’t tell you that it was “lesser” and you shouldn’t do it. But your tone reads (to me anyway) more like you want UMich but just worry that it’s too risky. If the whole appeal of Nova is risk-abatement, I’d say, bet on yourself and go to Michigan. Easy for me to say, I know, but JMHO.