The surviving party members would have to leave the dungeon to find the 1st level cleric, and then re-enter. The section on this on page 45 infers that the party would then leave the dungeon - ie "cast the spell and then move out of the dungeon". You would then just start exploring a new dungeon instead.
Not to mention, under the Things to Remember section, it states that, once you leave the dungeon, if you re-enter, ALL of the treasure is gone. When you combine that with the rule for Rescue Missions (which requires you to leave the dungeon to find a temporary cleric), this means that your only incentive is to get in and get out with your petrified teammate.