I don't mean to be an asshole, but nobody guarantees you that your videos will stay up perpetually on YouTube. Especially if you've got hundreds of private or unlisted videos, it doesn't particularly surprise me that YouTube would pull them down, even if only for petty reasons. If you've been following the state of their website over the past few years, this sort of behavior is becoming quite common, and even among YouTubers with millions of followers I don't think I've seen them reverse a claim of this scale.
Yes, it's a shame. If you don't have them on your own computer though, then are they really yours? It's a hard way to learn that local backups are important, and "the cloud" isn't a panacea for your storage needs.