If GP is brought back, I don’t think you’ll have to worry about Marcus for too much longer anyway. He doesn’t have nearly the banked goodwill and track record to survive two years of this offense because he won’t fire his friend.
Really doubt MF brings Parker back. I know there's a lot of consternation about the lack of a public firing, but for all of MF's faults (in-game management, not bringing in a transfer QB last year, the Ludwig optics), one thing that he has demonstrated thus far is he wants excellence from his coaching staff and gets it - he has made a lot of excellent hires, and I'd argue every member of this staff apart from Parker has been good to great. He let Elston walk after years of being a well respected member of ND's staff, because he thought he could do better (and imo has) with Washington. Thus far, his only misstep has been making Parker the OC - and there's certainly some question as to how much fault he holds in that situation given he wanted someone else and the administration balked on the financials.
It's possible that silently demoting Parker is the best way to go here. Maybe he is doing his best to try to bring Parker back as TE coach, or at the very least allowing Parker to save face. If I was a prospective coach, I would certainly want to work for a guy that publicly takes the heat and gives me cover even if I've been demoted.
When it comes to coaches, maybe MF isn't as dumb as a lot of people seem to think. That being said, if Parker is OC in 24 then I'll be as upset as the rest of you.