I don't think Google is in a position to "replace" Android. They simply don't control the hardware; they can ship Fuchsia to their Home assistants and thermostats, but when it comes to phones and personal computing devices, they don't have many cards to play (beyond Pixel, like 0.5% of the Android market). The power lies with hardware manufacturers and developers.
Their new wearables partnership with Samsung may help here. Maybe Samsung would play along with a new Fuchsia phone OS. But there's still the developer issue; any new OS like this would need Android-backward compatibility support exactly similar to what Microsoft is doing here. "Android" in this sense doesn't mean "the OS"; its the application system.
What's happening in the Android world right now is so healthy and excellent, I almost can't believe its the product of Big Tech. Google is already pushing Android apps on ChromeOS, now Microsoft has them on Windows, through the Amazon app store, and nowhere in any of this is the actual Android Operating System. The comparison here isn't Android vs iOS vs Windows; its Android vs Flutter vs Web. Its a new way of writing "native"-adjacent multiplatform applications; the OS doesn't matter anymore.
Sure the touch-friendly UI will suck in some applications, on some deployments of Windows. That's not Android's fault; its on the developer to recognize the input method and canvas size, and adjust accordingly. I hope more do!