In Eastern Europe there are a few places that an emulated Tesla server software is being run. And you can buy a car, say from US, and they will patch (hack?) it to use their server. I don't know how good it is feature wise, but it is good enough that the cars drive around.

So to your point - you can probably use a car after the manufacturer is gone or stops supporting a vehicle. But this comes with a risk of trusting these not very legal enterprises.