1. Plot-forming characters do not disappear from the game and battles with them can be virtually endless (if you are not too lazy to visit them every game day). But demon generals disappear from the game world.
2. No, because there is no point in doing something too complicated. At least, at the moment.
3. Here, a lot depends on understanding the game mechanics. If the player understands the principle of the game mechanics, then no special commands are required. It may be relatively difficult only with demon generals.
For example, you can trust Nel to increase the character's level, as well as friendship levels, and then you yourself will be able to collect the missing treasures in locations with monsters, having a high character level.
Information about the mechanics is not a secret : Deimus described it in the books that are available in the Agranor library.