Unless he retires at the end of this season, that's what I see happening.
Hamilton will only retire when he stops being near the front. He's only 35, there's plenty of life in him yet, and F1 drivers can go for longer than in other sports. Mansell was 39 when he won the WDC, Prost was 38 when he won his 4th, Schumacher was 37 when he retired for the first time and then regretted it.
If the 2022 Mercedes is rubbish he might lose interest, but not before.
As for binning off Bottas for Russell, I don't see it. Yes it gets Russell experienced to replace Hamilton, but having him in the Williams mostly does that without having the issue of destabilising the team by bringing in two new drivers in quick succession. If/when Hamilton retires simply plug Russell in his seat, but keep Bottas for solid consistency.
I can see Wolff winding down next year, taking more of a back seat ahead of 2022. But with as many talented people as there are at Mercedes, I wouldn't see much changing if someone like James Vowles moved into the big chair. Mercedes will eventually be caught, of course they will.