I wouldn't call it normal, but it isn't unusual for him to disappear, if he gets damage going through a surface, or hit accidentally when you are moving things around when looting, etc.
If you load previous saves, you should be able to find when he disappeared, which may narrow down where, and what happened, depending on how much time there is between the last was where he was following and the first where he was gone.
If you wish, and you are playing on PC, you can email supportdos2@larian.com with your latest save (or a Dropbox or Google drive link, etc), and I may be able to find / restore him in the developer build of the game. If you are using any non-Larian mods, also include a list of those enabled and/or the modsettings.lsx file from your profile folder.
Each save is a folder in the '..\Documents\Larian Studios\Divinity Original Sin 2 Definitive Edition\PlayerProfiles\<ProfileName>\Savegames\Story' folder.
In Windows Explorer you can zip a file or folder by right clicking on it/them and selecting 'Send To | Compressed (zipped) Folder' (and similarly in OSX/Finder).
