It really depends. Is it truly clickbait as in, the thumbnail is ice cream but the video is about baseball? Something really outrageous and obvious like that? Then yeah, I probably would unsub!
If the thumbnail is just a little exaggerated or only emphasizes one part of the video, that wouldn't be enough for me to unfollow if the video was good.
Er, I'm referencing videos here since video clickbait is what I'm most familiar with, but in terms of comics, if the cover or chapter previews for a comic are like, a completely different style or the quality is really different from the actual story, I bounce almost immediately. The same goes for games.