Me and two friends were trying to knock out some lvl 10 leves in Gridania's Emerald Moss camp, and we realized that even though we could kill the targets with no issues, the 'Lone Wolf' mobs that patrol the area were just too much for us to handle. I was the original holder of the leve, and with seven minutes on the clock, I abandoned it at the crystal. Realizing that my MP was down to a quarter, I connected with the crystal again, only for it to ask me if I wanted to join in on the leve that the party leader had. I hit yes in wonder and was brought back into my own leve, with now six minutes on the clock. So if you have people lose connection and they run back to the crystal, they can re-join the leve!
tl; dr; > As long as the party leader still holds the leve, you can go back to the crystal and re-join the quest if you get kicked out of the game.