Organisations are made of people. There are enough people who care about Mozilla's mission that they'd do the things even if Mozilla didn't, and if they got together they could get at least 10% of the funding from non-Google people who currently donate to Mozilla, if Mozilla ceased to exist.
The only real downside is that they wouldn't have a seat on the WHATWG.
In the open market, any organization that doesn't cares more about its survival than its mission will eventually be replaced by one that does. This is fundamental to the definition of "survival".
> If Mozilla falls, another will take its place.
The one that will take its place will be an organization that prioritizes survival, not its mission.