Well ok, not dead. Dead sounds final and I still think that we will get more IPv6 deployed in the future. And I set up all my servers as IPv6-first. So no, I don't think IPv6 is dead.

But I'd claim it failed completely. Many very public services (eg. github.com, sentry.io, office365.com, archive.org) outright don't support it. And the fact that infrastructure providers (like mobile network carriers) don't support it either, proves that it is far from "alive". In fact, I'd say it is deader than MMS, Fax and landline. For these I can still get service. For IPv6 (on the phone) I can't.