We know Michael Mulcahy owned at least one bar. We believe it was at 227 Hamilton Ave, as that's where he was listed in the Brooklyn City Directory before he was listed at 85 Luqueer St. He's at least once listed at them concurrently, so presumably one was home (85 Luqueer) and one was business (227 Hamilton). Also, 227 Hamilton Ave, when you look at the street view on Google Maps, appears to be a commercial rather than a residential building. (Things do change over the course of 120 years, though, don't forget! Further, a quick Google for "'227 Hamilton' Ave Brooklyn" gives rise to this article from the NY Times in 1879, which should have been when or just before Michael Mulcahy was there. It appears to definitely be at least partly residential. There's no saying that Mr. and Mrs. Dempsey didn't live above the bar, though!)
Michael Mulcahy was not working as a bar owner when he died in 1917. (He was a security guard, I think.) What we learned from the rather ambiguous "wife of a cousin" was that "Michael Mulcahy owned two bars in Brooklyn which he lost after they changed the beer." Betty and John, though, told me that they'd heard that the bar was lost when Michael's children took over the bar, as they didn't have the personalities of bartenders.
Third possibility that just occurred to me, since we don't know when the family stopped owning the bar: Could Prohibition have played a role in its demise?