Dorn Sidequest, just recruited him on my way to the Nashkel mines

Hi guys, my party was on its way to the Nashkel Mines when I had an encounter with a band of brigands and then Dorn showed up to help my party in taking them out. I asked Dorn to join and a new side quest was given to me with regards to Dorn to hunting down old party members. I am currently still in Chapter 2.

I decided to remove him from my party and take back Kivan instead. My question is do I still need Dorn to be in my party when I progress into the later chapters of the game, or can I complete his side quests without Dorn in my party?