(Re)Vanced is an app, dealing with googles backend.
They can either change the youtube app, to break Vanced, but this can be mitigated by not upgrading the youtube app, until there are patches for the new version,... or they can change the backend, thus breaking all the older youtube clients, making everyone upgrade their clients "now", which is a pain in the ass for many people.
For many devices it wouldn't be "pain in the ass", it would be straight up impossible. There are millions of devices, like smart TVs, that are out of support and don't receive updates, substantially changing API would break them. It might happen at some point, but it would piss off many people.
What I've seen is reducing quality available for older versions/protocols - so yeah, it will stay play but you won't get the highest bitrates without upgrading.
They can either change the youtube app, to break Vanced, but this can be mitigated by not upgrading the youtube app, until there are patches for the new version,... or they can change the backend, thus breaking all the older youtube clients, making everyone upgrade their clients "now", which is a pain in the ass for many people.