What’s the current licensing mode? Can they fork their own version at that point in time and develop it open source ?

No Chromium fork developer not called Microsoft have the resources to maintain a web browser engine.

But focus on the license overlooks a more important threat. Google made Web Environment Integrity so services could require approved devices, operating systems, and browsers. Resistance led Google to remove it from desktop for now. But they kept something like it in Android. And they will try again.

Chromium uses the BSD license. Google could take Chromium closed source tomorrow without needing to change the license.