By choosing the option "Publish Later", you have to know that your video isn't on our servers yet but only on your phone.
If, for whatever reason (ie: not enough storage on your phone) your OS (iOS or Android) need to clear space and delete your video, well...it can. It's rare but it can happen.
Your videos may also disappear if you turn off your phone, or if you log out from the app.
We decline any responsibilities for that particular situation.
To avoid that kind of situation, try no to keep your videos too long and just spread it out!