Not only will sideloading via ADB continue to work, installing from most other third-party app stores will continue to work. The developers on the Amazon, Samsung, and Epic app stores won't have a hard time with the developer verification process. F-Droid is in a uniquely inconvenient position that they have a legitimate app store, but its design causes them to have a hard time with developer verification.
> won't have a hard time with the developer verification process
Unless any government powerful enough has reason to make Google reject developers. Hell, doesn't even have to be a government. Do anything that annoys Google, goodbye rights for your app to be installed on any Android. Why would you ignore the obvious and main caveat? It doesn't matter what store it "continues to work on". Google can revoke privileges overnight with little to no recourse for the developer, regardless of the merit of such action, the usefulness of the app, or how much people want/need that app. This is literally heading in the direction of Kafkaesque.
F-Droid is also the only one that does reproducible builds which is a big security feature. One that is precisely the cause of making this hard. But it also makes it safer than even the play store. It should really be accommodated.