Follow the steps in this guide to find out how to dismiss a Companion in Divinity: Original Sin 2 and where they go. Luckily, removing a Companion from your party is rather simple, and you can always go back to recruit them again if you wish. You can only have up to four members in your party, including your own, which means you may need to shuffle some characters in and out before you have the party setup you desire.
In Divinity: Original Sin 2, there will come a time when you may want to dismiss a Companion to swap them out for another character.
