I rather believe HTTP/2 will die when HTTP/3 is available.

After all HTTP/1 is very simple to implement and already widely used and optimized. It is usable for most of cases. Plus, maybe in the future, CDN can serve HTTP/2 to client while use HTTP/1 to read the source.

And currently web browsers still need to send Upgrade request in HTTP/1 to know whether or not a unknown HTTP server supports HTTP/2. I guess this will still be true after HTTP/3 comes out (alt-svc).