a had another example of an easy to avoid defeat here:
Too many leavers - Warhammer 40,000: Darktide / General Discussion - Fatshark Forums
so we’re back at the core issue every time: people getting tired of other players that join difficulties they have trouble with.
as for leaving no one behind, there’s the other variant where the spawn system breaks and game fails to put pressure on the players who rampage through the map, so you can retrieve anyone. but it’s not the rule and one can only lose a war of attrition.