This is hard question to answer because there are some sprinters who have good endurance and and others who you can't get to jog a 1 mile warm up. I have coached some pretty sprinters and I would say Mo in his prime could probably just get under 5 minutes. I only say that because Mo was good at the long sprints and was always in great physical condition. Mo did workouts to suggest he could have been a top 400m guy. Although, most world class short sprinters would struggle to break 6 minutes. Like Decathletes, Mo could run faster if worked on.
Btw - I once had a 10.5 sprinter on a bet beat a 4:10 miler in a 1200m. The miler cruised the first 800 and had about a 50m lead going into first turn, the sprinter closed the a gap little down the backstretch and made up about 30 meters in the last 100 to win.