Ability to remove people from quests

[TheAbyssalSight]

I've had a few experiences where someone will join in on a quest, either leave because they didn't want to take the quest.. Or a DM event will pop up and they'll leave to go to attend it instead. I understand events can just happen anytime, but you'll either have people divided with the quest still who want to do it. But they can't because half of the party ran off to do something else, or other people will do the quest and the person(s) that wasn't part of it will get the exp and gold for free.

I'm not sure how it can be done, or what it would look like but it's happened a few times recently.