Got some nice shots of him today - although nowhere near as good as this one, as it was very overcast and windy so the light conditions were not ideal.
I suppose if he keels over they can always replace him with one from elsewhere. But he(presumably) represents the last of the genetic line from the old London Zoo herd, at least as far as ZSL itself goes anyway. There are probably still some other Blackbuck in the UK that are descended from this herd also, though I know that others have been imported from Europe.