Well, you'd be wrong.
Rather than just speculate, how about we look at some
actual numbers.
Blizzard's segment revenue of $1.83 billion for 2021 (which includes all their game sales, service fees, micro-transactions, licensing, and the WoW sub tucked in there) comprises only 23% of ATVI's total revenue, yet could almost cover the $1.86 billion of ATVI's total product, operations, and distribution costs. The WoW sub is a drop in the bucket, and far exceeds any server maintenance costs. Hell, ATVI's game sales alone are almost double the operating and distribution costs.
ATVI's net income for 2021 was $2.7 billion after tax. Just to throw out a number here, and lets say the WoW sub accounts for 50% of Blizzard's total revenue (it's obviously a lot less). ATVI would still net almost $2 billion in income if they for some reason got rid of the WoW sub. We know that WoW was profitable enough in 2006 for Kotick to begin seeking out the merger, and at the time it only had about 6 million subs and no expansions, in-game shop, or tokens. With all the additional revenue streams that have been added since then you'd have to be pretty gullible to think that at this point the subscription is necessary for keeping the game going.
Remember, the $15/month sub cost was determined back at the start of WoW when there were a lot of initial investments to cover and Blizzard had no idea how popular the game would be. At this point, even with 20 years worth of inflation, the structure in place that keeps WoW going is far more efficient than it was when the game launched.