If all relays that you use disappeared then your profile would be gone. This probably would not happen in a short timeframe. This is why it's good to use multiple relays. This is also why it's good to run your own relay or download a backup from to time time. Realistically, your profile disappearing from all relays that you use probably won't happen. It's more probable that you would use a client that nukes your relay list or contact list and you need to restore from that mishap. This type of scenario happens often with new clients.