My understanding is that they just wouldn't get updates, but existing drivers will keep working, and since they're open source, they should at least remain functional for some time.

But it still is a shame, Vega is not that old, and Polaris was very popular. I feel like they might be intentionally cutting them out to try to cause people who were satisfied with those to upgrade.

This only affects the official AMD vulkan driver. Mesa's vulkan driver is still being supported, check if you're using that.

https://news.ycombinator.com/item?id=38032124#38035968

I'd think they'd have support through Mesa's amdgpu backend.