Creators are already starting to build their own platforms for hosting videos and many of these are quite successful unlike prior iterations from 10 years ago.
I would point to platforms like Curiosity Stream and Nebula, which are creator driven. Though I would not exactly call them Youtube replacements, as they are more just platforms designed for supporting specific creators more directly (akin to Patreon). These platforms are often advertised as in-video sponsorships, so going back to the original point, I do think creators would be very vocal if such ads were banned.