I once accept a mission to summon army of healer. The mission was complete by well pay BG. But the number of army Novitiate was over summon by out number the land earnings which my land treasury was decrease in time. I was stupid enough withdraw all my Gold in warehouse just to let my army flea until the earning is able to pay the cost of my army. As I see each day worry all my other army might flea out. Gladly I figure just send my over number army Novitiate to war until the right amount of army I am willing to pay. Within time, I build more trading house and upgrade them to max and got the right number of Army. I wonder if reality is as cruel as like this happen to my land.
That wasn't really smart... It would be more easy to keep farming your neighbours, to keep your gold pile big enough.
Your army will only disband, when there is no more gold left. If you producte 0 gold/hour, you can still have a MASSIVE army present at that city. Just farm/raid in your neighbourhood, destroy some runes, and sell resources you don't need atm. If you can't sell your wood fast enough for example, just use the "exchange" option.