Pornhub could start Videohub tomorrow and shake things up if they really wanted to.
Otherwise there's Odysee (bad name, linked to crypto but good interface) and Peertube (federated but searches aren't* so it will never catch on), but people aren't too fond of those.
* I know about Sepia Search. People shouldn't have to use yet another website to find the videos they want on Peertube. It's stupid.
Pornhub could do that, but there's a reason they haven't. Video delivery is insanely complex and expensive and consumer tolerance for advertising on those platforms is low. With no other way to sustain and income from it the only option will be loads of smaller sites or a paid site.
Yeah, sites like peertube will never catch on besides any small techy circles. Any alternative will have to be centralized, that's the only way they'll get ad companies to their platform. Without ad companies, creators will have to revenue and no incentive to keep making videos on that platform.
YouTube isn't "going away". What could happen is a lot of people switch to something better.
Just like a whole bunch of people have switched to Lemmy, which is better than Reddit. YouTube would still exist, at least for a while, just like Reddit still exists.