The PS4 servers aren't going anywhere anytime soon. With native PS4 BC on the PS5, the PS4 side of PSN is safe for a good long time.
Look, I'm not trying to defend Sony here. I wish they were paying me to shill for them, but no such luck. I hate Jim Ryan's stance on backwards compatibility. I was one of those holding out hope that the PS5 would come out with BC for all past PlayStation systems. That said, I still think this issue has blown up out of proportion.
If you really do want to keep playing PS4 games 15 years from now on your old consoles, there are ways to do so. It doesn't matter if the CMOS battery is dead or not, when Sony eventually pulls the plug on the PS4 servers (which IMO, will last a lot longer than PS3 did), you can still play your games. Which is why I don't get why people are so outraged. We're talking in terms of decades here. You'll still be able to play your PS4 stuff, just not connected to official Sony servers.