How would it? Google can't retroactively un-license the Chromium source, which is under various open source licenses that I'm almost certain all include at a minimum the right to host a fork somewhere.
Additionally, if you are concerned about MF3, your best bet isn't some outdated Chromium fork – it's Firefox.
Just to be clear, Chromium Legacy and Supermium aren't outdated, that's what makes them great. They work on outdated operating systems, but they track up-to-date Chromium.
I kind of assumed as much, but unfortunately that also most likely means that it'll lose Manifest V2 support at some point (not that upstream Chrome will keep it).
That seems to be the concern of some people commenting here, and I wanted to highlight that the two are largely orthogonal as far as I can tell.
Google can't take back the source but they can make distribution of binaries hard? Most Windows users are very dependent on pre-built binaries, for example.
And doesn't Google have leverage over Mozilla by way of their funding?
Additionally, if you are concerned about MF3, your best bet isn't some outdated Chromium fork – it's Firefox.