starglider I'm not sure how GOS making their own phone addresses the Android release concerns. If Google closes up Android, having a GOS phone isn't going to improve things.
Having an alternative to Pixel phones does, overall, make sense, but it's addressing a problem that's completely distinct from "Google decides to abandon AOSP." If that happens, there's almost no way that any small team could continue to reasonably maintain a hard fork of Android.
Google (hypothetically) deciding to shut down AOSP would not be the same thing as Google deciding they won't have any OEM partners -- that would basically mean that Samsung, Sony, etc., would need to individually or jointly fork Android or stop selling phones. Or, I guess, switch to HarmonyOS!
If Google (as expected) continues to license Android to other handset makers, and GrapheneOS joins with a handset maker, it plausibly would remain possible for a high-security Android variant to exist. Obviously there is no way to meaningfully speculate about licensing terms -- for a non-AOSP Google Android or for an industry fork of Android.
I expect people will speculate anyway.