Let's hope they are just trying to look like the good guys in the situation and aren't being serious .
In the short run they're free to continue to patch the latest open source android, I don't think Google can retroactively revoke open source licences.
In the long run they're free to make derivatives or better, be encouraged to divert their attention to a more permanent alternative such as Linux phone on a custom ROM adoption scale.
I'm not worried.
It's not really about the current open source version of Android, I am sure people would continue to update, maintain, and work on what is available. The bigger issue would be for people that like to run Lineage OS with gapps and Google Play. Eventually their version of Android won't be supported.
I'm not worried about it for my own purposes because I only use open source software and refuse to use Google products. I would just switch to whatever open source Linux based alternative that would become available.
This could be real shitty for the custom ROM communities based off AOSP.