How about this...:
A: Forfeit becomes an option when the Duty Finder commence window pops for the player that's queued. That way people can't just forfeit on other players all the time, since it's not like we can just make DF pop whenever. Especially those of us who have to wait 30-45 min to get a damn queue pop sometimes.
B. Let the player queued for DF simply hits commence when DF pops, and if everyone commences and the instance starts, the match simply ends if not yet completed. If engaging a player queued for DF in a match, a notification that the other player is queued for DF and could be removed from the match is shown.

Pretty simple ways to solve yet another game-breaking problem, in that we can't effectively use TT as something to do while sitting in queue... and this impacts both TT, as well as people trying to run instances who have this as a reason for parties to form and unform, and those who queue for something that's a stupid unnecessary long time like Frontlines in a party and time out because someone else in their party was locked in a TT match, impacting the entire party from commencing.