The store on South Main that Mather and Shortsleeves were working on the morning of August 4th was just a few doors away from the corner of Spring Street. The photo does not mention which street is which. If the trolley tracks in the photo are on South Main then the burned out building probably (almost certainly) contained this store. The street looks too narrow for South Main so the store was probably to the left off the photo.
I have never read of any of the family properties being destroyed by the periodic fires that swept through Fall River. I have read where the A. J. Borden building came pretty close once.
Harry, the following information about the 1916 fire was taken from a book written by Judith A. Boss,
(Fall River, A Pictorial History pages 136 and 157).
"On the eveing of February 15, 1916, a fire broke out in the basement of the Steiner Company building on South Main and Spring streets. The fire, the largest in the city since the fire of 1843, destroyed several acres of commercial buildings on both sides of South Main before it was finally contained. The total loss amounted to over $1.5 million.
The fire destroyed a large portion of the South Main street business disrtrict. To avoid a similar catastrophe the owners of McWhirr's got permission from the city to replace the buildings with modern concrete and steel buildings. The new store increased the floor from 6,000 square feet in 1886 to 120,000 square feet. McWhirrs department store was demolished in 1981.