You can resume and start there but as soon as you start a game before that waypoint it will be removed from your list when you select quest again. The public game trick is the exact same. You'll be able to start a3 after leaving it, but lets say you load/join an a1 game and go to start a new quest the A3 quest won't be there.

If there's a way around it, let me know. My friend said maybe you have to complete 1 quest in A3 to have it permanently in your list. Is this true? Yes I am another Balial inferno DH having a hard time. ><