My impression is that when a hotel reflags, award reservations generally aren't honored while bookings to be paid with money often are, although usually elite benefits aren't offered. Usually those with reservations are contacted as soon as the reflagging is announced, and future guests are permitted to cancel or to negotiate something, including being rebooked into a property in the old chain/family. Unfortunately reflaggings tend to be announced without much advance warning.

However, I've never heard of a case of a guest being kicked out suddenly in the middle of a stay (single reservation) due to the reflagging (or other ownership change) unless the hotel is being closed for renovations.

Bonvoy's hands are tied here and they did the best they could, namely finding the OP a room at a nearly approximately equivalent Starriott and not charging anything additional. In terms of compensation, I'm tempted to say no as it's not the fault of Bonvoy/Starriott, although I think the original hotel should have made the arrangements for the OP's award stay to be moved to a different hotel.