Not neccessarily. A spun off YouTube would still have YouTube premium and ad revenue. They could also sell user data to 3rd parties (I doubt Google currently does it on a large since it’s in their interest to have a better ad network than its competitiors). A move similar to Reddit’s with their API and exclusive search agreement or agreements to feed certain videos to AI would both fetch a higher price and upset the quality less since the vast majorty of videos watched are found through YouTube itself.
I think that’s how a large part of European languages still work.