Traditional desktop Linux heavily involves big tech companies including IBM (Red Hat). AOSP has a massive amount of non-Google companies and individuals working on operating systems based on it. It would survive without Google.

You're misinformed about security preview patches. It has nothing to do with Google being hostile. Additionally, our security preview releases have regularly included patches for components not specific to Android such as wpa_supplicant prior to those being publicly disclosed by the upstream projects.

I believe the timely security patch issue will be resolved with the Motorola phones due to the OEM partnership.

Long term in the future, surely the open source community forks AOSP itself and maintains it. The worst option would be giving up and trying to focus on Linux (desktop) imo.