It's also considerably cheaper to develop than WoW is. Each WoW expansion has an immense amount of content compared to the expansions and updates of other games these days. A "dead" WoW would still have a lot more active players than 20k most likely. Which is why Blizzard relies a lot on preorders and day 1 hype sales to support such a huge development project. I'm sure they are looking at ways to transfer the Warcraft playerbase to a game that is easier to maintain live service on, but retain a similar amount of players. A new game would let them develop on a more efficient engine that will probably be unified across all Blizzard games. A WoW sequel, or at least an analog of some kind, is almost certainly in development. Maybe it won't exactly be an MMO, but it will be something similar. And then WoW will go free to play with a broader cosmetic shop and lighter updates.