With Reddit shutting down its API setting a precedent in the corporate tech world (and Reddit was a major outlier in that a ton of their users are technical minded and support third party clients, YouTube does not have that kind of userbase and will not get backlash for it), Twitter doing whatever the fuck they’re doing, and Google already hellbent on destroying ad blockers, the days of Newpipe, Invidious, and Freetube are numbered. Wouldn’t be surprised if they implement Netflix level DRM tomorrow that makes alt clients impossible. I say savour your alt clients while you can guys, you won’t be able to soon.
Invidious doesn’t use YouTube’s API. It merely requests content from YouTube either directly or through a proxy. So, I don’t think it’ll disappear forever unless the developers stop working on it. It’s probably gonna be a game of cat and mouse where YouTube figures out how to break Invidious, and the devs keep finding a workaround.