"Even now, the amount of people who play Skyrim seven years later; millions of people every month are playing that game," Howard replied. "That's why we keep releasing it. If you want us to stop releasing it, stop buying it."
I don't see how Classic is any different.
There's the pent up demand for it in place, as is, #nochanges (cue chanting, bring in the pitchforks and torches).
It's a fine distraction for existing WoW players to jump over when they're bored of retail.
It's pristine nature is a key to its draw.
TBC, and Wrath are not as necessary to be redone simply because they didn't suffer the Cataclysm. Vanilla did. Vanilla got rebooted. Everyone curses BC and Wrath questing because they have not changed. The classes have changed, experience for leveling, etc. But the story, the world, the drops, the gear, is mostly the same (save for the global affect of the squishes).
But Classic, Vanilla -- it's pretty much gone in the current game. That's what makes Classic compelling. As it was, warts and all, as best as they can make it.
Classic, static Classic, will make plenty of money. It will pay for itself the day it's released, it will continue to be profitable either with dedicate subscriptions, or simply good will. It's maintenance burden is low as it's mostly technical engine testing changes that they have to keep up with, they don't have to develop new content, new art, new story, balance attributes, create gear, nothing. They just need to ensure that the sound works and the pixels are the right colors in the right places on modern hardware as the computers change going in to the future.
And just think, if in 5 years, they need an ARM port of WoW? Classic will come along "for free".
If you as a player are bored of Classic and no longer want to play, it's no big deal. It's OK to leave and play something else. I haven't been to Disneyland in years. Years and years and years. I have friends with annual passes, one friend is a total Disney geek. But, nope, not for me, no matter how often I used to go when I was younger.
I will tell you this.
Disney is not missing me.
Blizzard won't miss you if you leave Classic. They will wish you well, and simply let you know that the light should still be on if you ever want to just pop back.