He might also just be very busy and he puts the guys where he is getting the most money from. As long as your contract doesn't state when the work needs to be finished by and he has someone there working, there isn't anything you can do unfortunately. He needs to abandon the site entirely before the state will do something. Now you have to weigh how long it will take him, vs waiting for someone else to be able to get there and finish it, then factor in the added cost of the new crew vs what you're losing in revenue waiting for him and see which one works out better financially.
If the shower is the last thing on the list for a rough inspection, then yes, he has to finish that before he can do anything else further in other areas. Now that I am thinking of it, if they just discovered that a shower can't be placed there, then he is still in the rough inspection stage? If so, he is about 30% done with that are. If the shower was fully built before it was caught that it wasn't legal, I have serious questions about the ability of the inspector who signed off on the rough inspection (or if he got one).
How much was the job in total? Normally I charge for any special order materials up front, first day of work (demo) I get another chunk to cover labor and materials for the week. Then everything is on a draw schedule based on milestones. Framing signed off gets xx%, rough plumbing and electrical gets enough to cover my labor, materials and the sub contractors to that point, insulation inspection sign off another check for labor and materials or subs, once the sheetrock is up and finished is another check, flooring done is another check, etc. Unless the job is only going to last a month, that payment schedule isn't broken up enough for my liking. Also, I leave 10% once the job is completed just for the punch list. Then the home owner can have a day or two and walk the place, make sure everything is working and good, then when they're satisfied I get the final payment. I understand the draw of front loading the payment schedule to make sure the home owner doesn't decide they ran out of money and can't pay you now, but 70% of the money when 40% of the work is done is way too much up front unless they're installing a ton of high end, special order cabinets and trim.