Give them a reason not to leave or afk. One idea is for every x strikes you do without leaving you get a care package which can be sold for rep or glimmer or exp. Performance could play into this by making the care package have a chance to drop bonus stuff based on your performance in the strikes up to receiving it. Another idea would be to simply make a rep or exp bonus at the end that increases every strike you do without quitting in a 24hr period. Cause honestly I have NO reason to do strikes unless they relate to my bounties so yeah I quit what I don't need generally. But I don't complain cause if people quit on me I just solo it.