Each run will require the player and the caravan to face as much as four random encounters, determined randomly according to the trade route. Each encounter has an invisible kill counter, which goes down with each hostile killed. Once the counter is at zero and combat ends, the leader gives the all clear signal. However:
Brahmin killed in combat will decrease the pay out. Particularly poor performance will ban the player from subsequent runs. Good performance will result in a $500 bonus.
Every single critter and character marked as hostile has to be killed to receive the all clear. This includes hostiles who don't initiate combat (like New Reno mobster encounters).
Note that eg. Den slaves are not included in the kill counter, but will count towards it when killed. As caravaneers will kill them, this can reduce the counter below zero and cause the caravan to become bugged.
Leaving the map before the all clear is given will count as abandoning it and dump the player on the world map. This will also ban the player from subsequent caravans.
If the caravan leader is killed in combat, the caravan will complete and a stand-in (Velani, Ferndown, or Nording) will pay out the player's wages. However, they will be unable to go on any subsequent caravans on that route.