The long tail doesn't matter. Once IPv4 traffic is a small fraction, the big transit providers will make it cost too much to bother with, and their customers (retail ISPs) will just cut it.
Only global IPv4 matters. If in fifty years there's still a device that insists on speaking IPv4 with the address 10.20.30.40 that will still work and it still won't matter to the Internet any more than it does now.
The appropriate comparison is leaded gasoline.
In my country this was never formally banned. You can't buy a new car which consumes it of course, they banned that, but the fuel itself is legal and for a while enthusiasts would travel to a retailer which still sold it, there might be one in the next town, or the next. Of course with fewer customers the price went up, further reducing customers and squeezing more retailers out, soon enough you might have an hour's drive to buy fuel. The wholesalers were next, if you sell a tanker of ordinary unleaded every five minutes, and a tanker of "high performance" unleaded every hour, why bother making the leaded fuel that shifts only one tanker per week across the whole market? It's not even worth reconfiguring your mixers to make it. So you mark it "No longer available" and gradually across the market the retailers can't buy more and there is no more leaded gasoline.
You can make your own leaded gasoline, but the volumes involved mean it no longer makes any meaningful difference, you could make your own lead paint too, if you're crazy, it doesn't make a noticeable difference to the world.