Flutter is different as it is 100% OSS so if Google cancels it, its development could theoretically be continued outside of Google. Of course, this depends on the presence of enough demand for that. Mozilla has laid off their full time Rust staff (including some people whose actual responsibility was different but they still contributed to the Rust compiler) and the Rust project survived. Instead these people got hired by companies like Amazon and Futurewei. Some are less involved in Rust now, some return. Some risk remains though, as if nobody is using Flutter, nobody will keep it alive.