Russel will be the new Mercedes's top driver in the next future.
I wish you're right. But I fear that this won't happen this soon. Hamilton likes to have some drama around him, this makes the newspapers write about him, show his picture, show his sponsors...
There are some 5 (maybe more) drivers now in F1, some are even my favorites, which should - sooner or later - make way to newer, younger ones. I expect Formula 2 and Formula E has quite a number of drivers that could fill those spots in the blink of an eye.
As if that wasn't enough, we are going with brand new car design as well, which will make it harder for drivers to adjust to it as well, I do not expect clear Hamilton or Verstappen domination at the start of next season, which means that if Hamilton at his age doesn't get used to the car quickly, can't get as many points as we used to him getting, and still spends too much of the cap Mercedes has, then he may retire after 2023 reasonably.