So, by your own logic, if Microsoft ends up in a disagreement with Google about the direction of chromium, whats to stop them from just forking it and becoming the new dominant engine?
Chrome will only remain the dominant web browser as long as its users view it as worth the hassle. If Edge is built upon chromium in the future, I'm not going to sit here and say that Chrome will remain the dominant browser following that.
We can sit here and talk about 'what ifs' all day.