Current questions and answers regarding the map editor.

Please tell me what I am doing wrong.
Zehir dies, but the quest doesn't fail, and the game continues.

Your check is only performed once – at the beginning of the game.
To have the check run throughout the game, you need to place the condition in a loop.

function CheckAlive()
	while IsHeroAlive('Zehir') do
		sleep(5)
	end
	SetObjectiveState('kill', OBJECTIVE_FAILED)
	Loose()
end

startThread(CheckAlive)