What is the off chance that Google will drop Flutter?
This matters only if Flutter is a closed source project – but it's not. You can fork it on Github right now and continue working on it even if Google pulls its engineers off. I'd assume that those of us (and there seem be a lot of people) invested in it will continue working on it.
It certainly matters. Without a team of dedicated developers maintaining the project, the APIs it depends on will become deprecated, and it'll slowly become unusable.
Flutter touches a lot of APIs across many platforms. It's a complicated project that needs to support virtually every popular operating system in a visually and behaviorally consistent way.
Flutter also depends on Dart's maintenance, which is another project without significant open-source contributor activity outside of Google employees.
> I'd assume that those of us (and there seem be a lot of people) invested in it will continue working on it.
Having contributed fixes to Flutter and Dart, Google does not go out of their way to build an open-source contributor community around the projects. I would be surprised to learn that any significant support is provided by open-source contributors to Flutter or Dart.