Scripts

Not exactly a trigger, but you can do it like this:
function lost_PL4()
if GetPlayerState(PLAYER_4)~=1 then
.....................
end;
end;
and we attach the 'lost_PL4' function to a trigger that detects when a player loses a hero
Trigger (PLAYER_REMOVE_HERO_TRIGGER,PLAYER_4,'lost_PL4');

either 'obj1' has 'false' in the 'Ignore' parameter, or your task is recorded not in 'objectives', but in 'scenario informations'

The trigger didn't work. I'm confused by "~=1". Should I have replaced it with something else, or was it supposed to be written exactly like that? It didn't produce any errors, it just didn't work.

The original idea was to have the quest completed when two towns are captured, but the script I found in another map didn't work. Maybe we can come up with something here?

I replaced 'false' with 'true' in all objectives. Now, when that quest is completed, the player receives a defeat :(.