If a home base is attacked and the armies inside are defeated, the city(s) the user has occupied become unoccupied. If there are no armies in the home base, then defeat is immediate.
Armies in the cites that become unoccupied are not lost. Maybe they could be expelled to the outskirts of those cites, or automaticaly sent back to the user's home base (taking the travel path and time).
The home base isn't lost.