He's at the Office by Allan Gurganus

"Till the Japanese bombed Pearl Harbor, most American men wore hats to work. What happened?" This story is about a father who spends an inordinate amount of time at the office -- a workaholic you could say. He is also what I would consider an anachronism (a living relic of the past). "Since June of forty-five it's been All work and no play makes Jack." He is still working at eighty and had to write his own notes to remind himself about simple information.
"Forcibly retired, my father lived at home in his pajamas. Mom made him wear the slippers and robe to help with his morale." Mom and son set up her sewing room as his new office which he uses just like he did with his real office. "And, son? Along with the bad news, I think there's something good. He died at the office."