C# (and other .NET friends) aren't dying for a while, there's a large base of things written for multiple platforms on it, even though I think Microsoft isn't writing bunches of their core OS components in it.
Java isn't dying for a while either - anyone who still needs to support applets aside, or corporate applications written when Java was the fashionable thing to ship apps in, Android's install base will mean it's relevant for a fair stretch yet, even if OpenJDK fell into the sun tomorrow.
Swift I don't have much insight into, as I haven't done much with OSX or iOS in a while, and I have indeed not seen much uptake outside of those.
Which languages are you suggesting were/are good targets?
Python is technically not one company driving it but a bunch of developers on it are employed by large companies to work on it.
JavaScript is seeing a bunch of use in a great many places, but originated with one company's implementation and development.
Rust is pretty obviously one company's child, even though it is seeing decent uptake from other users. No predictions on whether it would survive said company dropping their work on it, though.