I guess the sort of people who stop at the end of the runway in this type of situation are the same people you see coming to a stop when driving their cars every time they see a blue light behind them .. regardless of whether the ambulance can get past.
The objective is to get assistance to the subject as quickly as possible, unless you see a set of steps and a paramedic at the end of the runway, taxi back to the apron or gate sounds like a significantly better plan.