Keep at least two full sets of your video files in a way that assures they won't be accidentally deleted.
Your computer can mark digital files "read-only" to ensure they're not altered. One copy should be protected this way.
If you don't use a computer it's still a good idea to keep one set of the video files on a storage device which a computer can access.
Additionally, I will hold a full copy of your project for sixty days or ninety days, or even longer if you ask. At the end of this safety period I will check with you before finally deleting the copies of your videos in my care.
When your project is finished, and the full size of the files is known, we can determine your best options for file storage. If you need more storage space I can help you find it.