I'm more worried that if Fuchsia goes, Flutter will go with it too. Flutter is actually a useful framework.
You'll end up with a huge legacy codebase and dart devs that are useless for most other platforms.
I do expect there will be lots of $$$ rebuilding legacy flutter apps in SwiftUI and Jetpack Compose
Facebook also realized that they had to go full native a long time ago.
You should always worry when your platform vendor doesn’t eat their own dog food. Besides Flutter will always be behind tsking advantage of the latest iOS features - especially if Google doesn’t depend on it.
This is also one of the major complaints about some of Apple’s APIs especially on the Watch. Even worse, Apple has specialized equipment that makes Watch development faster than it is on the outside.
(Disclosure: I work on the Flutter team.)