I don't think there is anything you can do retroactively to force the installation of a sprinkler system. How extensive was the fire damage? If they had to perform a Level 2 Alteration per the Work Area Compliance Method, then a sprinkler system would likely be required if the situation conforms to one of the conditions provided (IEBC Section 803.2.2). However, the Prescriptive Compliance Method would not require the installation of a sprinkler system. Also, the IFC does not require the installation of a sprinkler system in an existing Group R-2 building.
Otherwise, get an ordinance passed that requires the installation of a sprinkler system for Group R-2 occupancies (or any occupancy group) when a fire event is recorded on three separate occasions that cause more than $X of damage for each fire event or involves two or more units.