Forgive me if this has been asked.
Obviously Blizz can’t remove a class, that’s just not a reasonable option. But after everything that has happened, why do the factions still tolerate Warlocks running around summoning demons and messing with the Fel? Is there a lore explanation for Warlocks still being in the game, or is it something where we just kind of ignore it because we have to?
We are far too useful to be discarded.
We have our own Warlock planet with an army of Demons ready to defend Azeroth. We are satisfied with the status quo and don’t wish to take over the world or stuff like that.
But in the words of Shadow the Edgehog, “if the world chooses to become my enemy, I’ll fight like I always have”.
Why would you make an enemy out of Warlocks and fight their Dreadscar Army when you can… not do that and have the help of the Demon Army if things go south?
Because those warlocks are on our side. Warlocks aren’t really parading their demons and fel down the street, they keep to the shadows and secrecy. But they’re very capable people and handy to have around. It doesn’t mean they’re all straight evil or ever sided with the Legion.
So long as fel exists there’s going to be those who use it and demons too. It can be as taboo as people want, but the practice will never die. So easier to just overlook it and make use of it so long as they don’t get carried away.
My my, such precipitious commentary directed at the fel community.
Stares into the OP
Warlocks and DHs are evil, but we aren’t that evil now! 
The Black Harvest managed to steal enough demons from the Legion and bind them to eternal servitude, past death. Demons might also have chosen to become a part of the Black Harvest’s servitude to gain that immortality - or even in hope of continuing their purpose of opposing the Void through mortal means.
Soulstones, Healthstones and Summons.
Obvs.
Why are there still Death Knights and Demon Hunters? Those are far more pointless lore wise than Warlocks.
The Legion is shattered, Sargeras imprisoned and Illidan gone. Their purpose for existing ended with Legion. DK’s carried out a vendetta against Atrhas LK.
Warlocks are simply mages that have persued ever darker, more volutile and descructive magics. Their schools being Void, Fel, and Fire primarily.
It would upset Mortis was the official word I saw somewhere on a nondescript website in a nondescript building.