Singleplayer games aren't going anywhere. Last year we had the heavily SP oriented experiences God of War, Red Dead Redemption 2, Spider-Man, Assassins Creed Odyssey, Shadow of the Tomb Raider, Monster Hunter World, Far Cry 5, Hitman 2, Forza Horizon 2, and Detroid.
Then there were many indies/smaller games like A Way Out, Mega Man 11, Return of the Obra Dinn, Celeste and much more. And it took me a while to dive in, but nowadays indies are just as, if not more, content-packed than games from the classic eras. I played Hollow Knight and Celeste next to some SNES classics that were new to me and both of them have more content than a lot of those SNES classics and are just as good.
And this year started with Resident Evil 2, Devil May Cry 5, Kingdom Hearts 3, and Sekiro Shadows Die Twice.
Most of the games I mentioned seem to have been a good to great financial succes, so the market is healthy enough which means companies will keep investing in Singleplayer titles. And actually, I think the model of games like Anthem, The Division etc. will not be sustainable if all companies pursue the same goldmine (I feel like Sony knows this, hence their SP focus), especially if free games like Apex and Warframe are superior and even have a more fair economy despite being free.
The only thing modern MP games really took away (for me) is playing on the couch with friends. I now do that online, despite one living right next to me.