Scouting the rival splits the party in the next map. Companions get taken if adjacent to the rival, otherwise Piper gets taken and you play as the companion. Scouting with 1 open tile around the target will guarantee that Piper is chosen, while scouting with 2-4 guarantees that his companion is chosen. Only your final scouting action counts and as of v2 spells can also trigger this interaction.