I don't think that you'll lose much endurance. I'm training for a half marathon - I'm supposed to do 3 short runs during the week and 1 long one on the weekends - sometimes I can't do the 3 short runs (or any short runs during the week) and I've been able to up my mileage each long run. It's not really a problem.
You need to give your lungs time to heal!
