In my opinion, the current system, where the remaining, unkilled guards attack again until the player defeats them all, and only then receives the guarded item, is the most logical and suitable for most situations. But, of course, it could also work as you suggest. To reduce morale, you could add a recurring event before this. Also, in WoG, it is probably possible to use scripts to create guards that infinitely spawn in one location (although I don't know how to use scripts myself, and I only make SoD maps; but anyone can play them).
Regarding tents and their guards: I recently considered this aspect for one of my future maps. For example, you could make it so that each player has a tent of their color on their territory, guarded by troops. Another option: garrisons of different colors, belonging to different players, in front of the tent, with unremovable troops. Then, each player can freely pass through the garrison of their color, while others will have to fight it!