It sounds like you have a fun few sessions as the PCs together fend off various attempts to wrest control of the town away from the current king (surely there are other claimants to the throne, hostile neighboring towns, a glabrezu looking for a glorious victory, or whatever). You could easily exhaust a majority of the town's liquid assets fending off such attempts.
Assuming that the king stays as such, he then can pass detailed control of the town to a hand-picked viceroy (see also seneschal or vizier) who will handle the daily administrative tasks of running the town while the king goes off and does whatever it is that he likes until the town is once again threatened.
Any time the king directs members of the town to do anything that is really not in their interest (like empty the treasury to buy fancy magical things for himself), interpret it as an opportunity for his leadership to be contested. You could even create a recurring villain who would seek to exploit any political mis-steps ("Well, G'loxth says he'll tithe half what the King does, and I'm sure his brain-eating habits are simply lies spread by the King.").