No, I killed them all (plus the one lurking in the area to the right of the main ground floor) , which was one of the two things I needed to do, but the other thing I have to do is to find this item which is supposed to assist Robert to resist his zombification. Of course had I opted to kill or abandon Robert then I wouldn't have had this problem.Not familar with that route, but you should have to just kill all infected on the second floor then head back downstairs into the basement.