Current questions and answers regarding the map editor.

Try replacing the function that checks for clerics in the hero's army with this one:

function CreatureShouldSurvive(hero, id)
    while 1 do
        sleep ( 10 );
        if GetHeroCreatures(hero, id) == 0 then
            SetObjectiveState("zadanie4", OBJECTIVE_FAILED);
            sleep ( 10 );
            Loose();
            break
        end;
    end;
end;

P.s. This is the skeleton of the function that checks for the presence of a dragon with Ilia in Lords of the Realm.

And as another option: move AddHeroCreatures("Mardigo", 10, 1); above startThread, i.e.:

AddHeroCreatures("Mardigo", 10, 1);
startThread(CreatureShouldSurvive, 'Mardigo', CREATURE_CLERIC)
AddHeroCreatures("Mardigo", 1, 40);
AddHeroCreatures("Mardigo", 5, 10);