That shouldn't be a problem as long as you can still download apps from the Play Store itself (not the official app). Basically, take a look at how proxy stores like Aurora work, they connect to the Play Store servers and allow you to download apps directly from Google, without needing the Play Store app.

Of course, this doesn't mean that the downloaded app will work on such a device (if it doesn't have Google Play Services), but at least it lets you download the app, which isn't much different from downloading it from say, APK Mirror. And as long as you can extract the apps from either the Play Store or Android devices itself (via adb/root etc), I'm assuming sites like APK Mirror will continue to exist.