Not only WhatsApp video but also photos, messages, call logs, contacts, reminders and so on can be lost due to various reasons. In such case, a
Apple iPhone data recovery [joyoshare.com] is pretty critical, which helps to restore data from our device and backups with high success rate in 100% safe. Anyway, it's important for us to back up data regularly to keep backups and avoid data loss.
Related:
How to Retrieve Deleted WhatsApp Videos from iPhone [joyoshare.com]