[Cohen]

Well probably you should go for some options:

Dismiss A:
The troops aren't payd anymore and start attacking the current province they're in, but pillaging the province even before any battle occurs.

Dismiss B:
You want to pay your veterans, you spend X gold for piece (based on unkeep cost), and they raise the currently province where they're locate population by Y where Y are the soldiers dismissed, and IF the soldiers are national troops of a certain quality (ie crippled elite and so on) the PD of that province raises of a Z amount (they can train better the commoners levying in that province).

I'd add a feature when you cannot pay the unkeep.
If a troop fail his Morale Check it deserts as usual, if a commander fails a MC all his troops under command and him become a new mercenary company with the name "*commander's name*'s* *asset of randon names*" ... like Fighters, Warriors or according to the troops he's commanding.