Replacing a great HC, when they have plateaued, is tough. Odds are against you.
The expectation should be things won't be as good or as easy from here on. It's likely the next coach goes below .500, something that normally doesn't happen here.
A good example is what happened to the Bills after they got rid of Levy. They brought in the former DC (Wade Phillips) and tried to rebuild the old dynasty.
It rarely works like that. Then they cycled through some bad coaches, and finally became good again.
Same thing with George Karl. We got rid of him because we were tired of underperforming in the playoffs. The next guy fixed that by just not getting to the playoffs nearly as much.
As a Husky, getting rid of Romar (because he was underperforming given all the great talent he had) made sense. But we stopped underperforming because of our talent by just not getting much talent anymore. Now few are disappointed by UW basketball losses, because few expect them to win much anyway.
If you have someone that basically builds an era for a franchise, you usually don't replace them and reload. (I can only think of that working once, when SF got rid of their SB coach Walsh and Seifert became a SB coach as well. You COULD argue that it worked for the Steelers too...but probably not)
What you do is reset expectations, and spin the wheel a few times until you land on another winner. That can happen quickly (49ers) or take a long time (Bills), or even take decades (Browns, Bears, & Skins/Commanders).
It would be a tall ask for JS to somehow beat the math, the trend, and what is probably the reality. But you never know.