Sorry to hear about your buddy. I've bruised my heal pretty bad before and that hurt like hell and took a couple months to feel better. I cant imagine breaking it.
I've had 2 sets of fresh rubber mounted at the track (One set P.P. and the other were Qualifiers) and everybody I spoke to at the track (tire rep, other riders and track employees) all said just go ride. Take it easy like your warming up a set of cold ones. 1st lap easy, 2nd lap moderate and 3rd's fair game. I know he was on the street but just a few blocks of normal riding should be enough.