Well, there isn't a general rule about this, so let's try to explain how we could overcome this.. I came up with the following solution:
Create a new youtube channel and upload your videos there
If you, like me, keep a saved copy of your videos on your computer (or smartphone), it'd take just a few hours to reupload all your videos (depending on the quantity, of course). If the file size is a problem, a good solution is to use softwares such as "HandBrake" which compress videos A LOT while keeping an excellent video resolution.
Have our own YouTube
This was discussed a lot in the past, and I could eventually really come up with something like this in the near future, but it'll involve an additional server cost I'm unfortunately unable to cover at the moment. If our community grows in the next months, I could really put in place something like this. Videos would be never put down in this case, and it would be a great addition, but it's still unavailable so we can't apply this.
Upload your videos elsewhere, too
There are alternative sites like VIMEO and DailyMotion, just to mention some. If your videos are taken down from YouTube, you can still prove you uploaded them during the contest if you also uploaded them to those sites.
We understand how difficult and frustrating it would be to have your YouTube channel deleted after all the hard work you put behind it, but it'd also be quite hard for us to verify each submission if the video is missing, therefore you should try to reupload them as soon as you can, if it happens, as it's the only way we have to verify each submission. A first step to fight copyright takedown was taken years ago when we introduced sbupload, and our files are safe this way, but for videos, we don't have other solutions for the moment, as we can't use sbupload to host gameplays as well, sorry.