On the Qt side, it looks like Qt clients are able to survive a compositor crash since Qt 6.6. I haven't personally tried this, as I don't recall experiencing any kwin crashes in the last few years.
As I understand it, in Wayland all the necessary state lives client side, so a client is free to wait around and connect to a new compositor. The compositor might not place the windows exactly where they were before, but there is nothing architecturally that forces clients to crash if the compositor crashes.
https://www.phoronix.com/news/Qt-Wayland-Compositor-Restart
As I understand it, in Wayland all the necessary state lives client side, so a client is free to wait around and connect to a new compositor. The compositor might not place the windows exactly where they were before, but there is nothing architecturally that forces clients to crash if the compositor crashes.