When you configure Failover there should be no disconnection of the camera. This is because Failover is designed to change your WAN interface, in case one of these fails. In other words, it works as a backup for the internet interface. Therefore it does not change any kind of configuration on the LAN, which is where your devices are connected. As this does not change, the IP of the camera does not change either. You should not lose access to it. As I said, if you have other settings such as Portforwarding, public IP access, it may be affected by failover.
If you want, you can send me the troubleshooting file before and after setting the failover. That is, before losing the connection to the camera and after. Just to check interfaces after the change. You can download this via System→Administration→Troubleshoot.
On the other hand, if you need to go back to a certain configuration after making some changes. You can do two things. One is to create a default configuration which you can do via System→Backup. After making the default configuration, you can go back to it by simply selecting Restore to user defaults on this screen. Another thing you could do on this same screen is to download the backup file of the device, with the settings that are currently made. If you have any kind of issues with the device, you can upload it on this same screen and it will be restored to its downloaded configuration. For more information about these functions, I leave you this link.