Sorry but you are massively overvaluing the value of Hamilton. Pick any driver on the grid and they would move to Mercedes in a heartbeat and I bet they would all be far far far cheaper than £40mil a year. That is a ludicrous amount to pay when you have such a dominant car.
You are completely ignoring the amazing talent in the rest of the field. Put Max in that car and see what he can do. Charles Le Clerc? easy title win. They would all move for a paycut if it meant being in the Mercedes.
You say that Hamilton adds so much value to Mercedes and sponsors. Does he? He's probably the most hated driver on the grid and very Marmite. Some love him, many hate him. I wouldn't want that as a sponsor.
And as previously said, Mercedes NEED to balance the books, jobs are going from Mercedes, how can you turn around and give Hamilton £40 mil or more when you could get a Max, Charles, Danny, George for far less. Try justifying that one to the Daimler bosses.
Mercedes if anything have been a victim of their own success. They are stale now. No-one is that fussed if they win another world title, they're expected to, but did you see the interest in F1 and Mercedes when George Russell was allowed to race just once. They need a fresh face in there.
Either cut Hamilton's pay if they want to stick with him or get rid. Both options would benefit Mercedes in my opinion.