The world is not moving on, IRC is very much here to stay. It works way too well for this sort of thing and people like being able to have their client set up exactly right. It's just heavy iPhone users that left and once Apple allows web push iPhone users will be back on IRC again.
I run ZNC+Palaver and get push notifications on my iPhone; but I also run ZNC on my own machine somewhere, which is a cost and a setup most people don't usually have to bother with.
One solution for casuals is probably IRCCloud; since IRCCloud will give you the same experience as mine for free, but will disconnect you if you're inactive (unless you're paying).
Irccloud also precludes all of the nice features you might get if you're running your own clients... so, YMMV.
I don't doubt that IRC is here to stay, but I've noticed more and more people moving from IRC to Matrix. Nix, the wgpu-rs guys, I believe the blender devs, and I believe the GHC devs are all on Matrix now.
(No affiliation, I just like the service)