I have been amazed at the little importance people put on this kind of video. You have video evidence of crimes with faces appearing clearly. It can take 5 to 10 years for such events to calm down enough to reach a point where crimes can be prosecuted.
And it is hard to blame youtube for that. They are considered the channel for Lady Gaga and silly cats video. Hell, I know 3 years old toddler who browse youtube unsupervised.
In many places Youtube is criticized to promote violence and extremism by leaving these videos. I feel bad for them, they are between a hammer and a hard place.
I just hope that the censored video are not totally deleted from their servers. They should have someone reviewing criminal videos and keeping them at the disposal of judicial authorities but even that opens a whole can of worms: do you obey only to US authorities (who do not care about war crimes in other countries)? Do you obey all world authorities including Saudi and Chinese?
Anyway, that's youtube's problem, not ours. Simply, helping prosecute war crime is not part of Youtube's mission, so do not trust them for it. To anyone who feels this is important content, use youtube-dl and keep backups. Make torrents of it, share it around, make sure it does not disappear.
And when some NGO finally realize that this content is precious, pump up your upload bandwidth and fill their servers.