Ending a "Surrounded" Scenario.
Yes, since the rule for ending the scenario is that if all the models are removed from one side in a turn and the rule for replacing models is "at the start of the next turn" then getting rid of all the Lurker models on the board nullifies any coming back.
Bad Place.
You'd have to ask Uncle Mike for an official ruling but I would say that the one Scene of Horror is free, since if you bought them you'd actually be getting D3 and having more then one invalidates the point of the special mission.