Though there is another thing I noticed... When I turned off the Wickerbeast and miniMAXIme mods, I lost the avatar and the inventory, rather than just having the normal player character back.
Simple solution: don't remove the mods! :-D
No, seriously: If you start up Factorio, the prototypes are built based on the active mods. If you disable both the character mod and the selector mod, the prototype created by the character mod doesn't exist anymore, and the selector mod can't do anything to resolve the issue – because if it isn't active it can't run. That's not a bug, that's just how things work …
So if you decide that you want to remove the selector mod (miniMAXIme or others), your best bet is to change to the default character before removing it. Of course, you still may lose items if your chosen character happened to have more inventory slots than the default character. In this case, switch to the character with most inventory slots, dump your stuff into a chest, switch to the default character, save the game and remove the selector mod.