I fully agree with your scenario as to why would the get rid of him and for mine your post clearly demonstrates the problem with having Flanno as the go to coach as it means we have to suffer Mc Humptydumpty for another full season and I wouldn't put it past him to do a lot of white anting in an effort to upset the apple cart.If the plan is for Flanagan to coach in 2022 I can’t see any reason to get rid of Mary. No coach that is worth having would take a one year contract, especially if they are then subject to the limitations that Mary currently has on him.
Leave Mary to do press conferences and video, and have flanno working on attack and defence while allowing him input into recruitment. Then Flanno can hit the ground running in 2022.
Otherwise, sign a long term coach for 2021 and let them do their thing.