What other open source browsers have been left without maintainence? Ones with no market share? As mentioned, Servo was never really finished and yet it has recently been scooped up by the Servo Foundation. Mozilla still very much maintains Firefox.

We have plenty of examples of open source databases, operating systems, libraries and languages leaving the major companies they were created at and being scooped up by a foundation or consortium to maintain.

WebOS is a great example. Created by Palm as a mobile OS before they sold it to HP, who open sourced it. Now the primary contributor is LG, who uses it in smart tvs.

But there's plenty of other examples in the open source world. Chromium is far too important, and there's already thousands of eyeballs on that code base. There would be a Chromium Foundation established very quickly if Google abandoned.