I saw another company fighting werewolves. There was 7 sellswords and 3 werewolves. I decided to join the battle.
The window with overview showed up: my banner and sellsword’s banner to the left, indicating that this will be joined fight with them at my side.
When the fight started there was only my fighters. When I finished off werewolves and returned to world map, sellsword’s group was standing just right there without any loses.
I’ve attached the game log. I think the start of the battle is somewhere around 23:11:27.