Hope he doesn't get a State Farm quote because they will be half of the premium of the expiring. I've lost a lot of plumbers in NYC to them lately.
Check if it's eligible for the Patriot program. They target NY plumbers. MGA that works with retailers.
I specialize in NY contractors. Utica National is a must, as recommended above. They can get down to like $110 payroll rate if the account is good, but not sure if they're down with that much subcontracted work. Sutton is going to be one of your more competitive options here, so if you have an indication, prepare for that to be one of your best. Also, look into USMC (Fortegra Specialty MGU) and Patriot Underwriting Managers (Trisura Specialty MGU). Travelers Select's exit from this market is screwing over a lot of people right now. Just not enough options for these mid sized folks.
Utica National does. Good job with this. They rate on payroll, not sales. Not sure if they would accommodate an open claim though. Other than that, NEC is probably your best bet I would assume.