Party Finder doesn't work in dungeons, we've found. So if you went in with a full pre-formed party, you can't add people from Duty Finder after the fact, nor can you get more people from Party Finder (because the dungeons exist on a different server, and PF is local to your own server.)
Kind of a gap in the system, but voting abandon and re-forming is pretty much your only option if you went in with a pre-formed party and lose a member.
Entering via Duty Finder if you're in a group less than the number of people needed for the dungeon, even if you are in a duo or trio, the Duty Finder will give you the option of replenishing a member if you lose a person.
Edited, Feb 28th 2014 12:38pm by Catwho