It would be dead. Google would shut it down or sell it, but who is going to buy billions of dollars a year in costs for no advertising revenue in return? Youtube's hosting costs would put a massive dent in even some hypothetical really nice billionaire's wallet. Apple could afford it and they'd run it a million times better, but would they even consider putting so much loss on their books for the sake of ... PR?
What percentage of YouTube's revenue do you think is from subs?
The slop is already there. Even without the slop, which it would be borderline impossible to identify en masse, the hosting costs are still astronomical. I appreciate your idealism, but Youtube without advertising revenue would be a financial black hole, and even if it survived, creators would simply be the ones taking the hit
Unless you're suggesting Youtube would just start again from zero, in which case it would just fail and it might as well be the same as dying