What would the airline do if you simply jump in a taxi and disappear? If you refuse to board the bus to LHR will you be manhandled on to it. Will the airline ground staff call the police and what will the charge be? Refusing to be kidnapped?
Assuming baggage has been released I think it should be up to the passenger to make alternative arrangements as they wish. It would be courteous to inform ground staff of your intention so they don't waste their time looking for you.
s37