Every permit I've pulled in other towns require the fire department (along with other depts) to sign off on permit checklist BEFORE you can even leave the building permit application with the building department. The 2nd line of defense against this mistake is have a fire dept inspection on the inspection card before the rough building inspection. Either of these procedures would have avoided the need to tear open walls and put them back together.
I've heard from the fire chief, who heard from the state fire marshall's office, and they will grant a waiver with 1 condition... that the windows are 5.7 sq/ft egress sized windows. We installed 2x double hung windows that are 4.6 sq/ft so the windows will need to be changed. The new windows (2 - 2x double hung) with material and labor will cost around $2,500-$3,000 for my cost. Better than a sprinkler system, but completely avoidable in the first place.
I'm wondering if the owner should just leave it as is and see if anyone in the town follows up. He could then threaten legal action against the building inspector for issuing a permit without this requirement and then signing off on the rough inspection without the sprinklers in place or a fire dept signoff. It seems common sense would say the building inspector is incompetent at a minimum if the town has an ordinance that all finished attics in homes over 35' need an attic sprinkler system. I'm not an attorney so I have no idea how that argument would hold up in court.
I think when you get the actual wording
It will have a lot more details on the requirements, then have been stated here.