Or, in the more current case, wait for a distraction like a fight and then steal the stone. Maybe one of you can throw a chair and get a full bar brawl going. That might prove enough of a distraction to get the shard and not have to fight this guy right away. Just to keep everyone together, I would suggest Hayden, Yeva, or Mira steal the stone while Tychus is busy with Enigma. Gharn can whip up the bar brawl by tossing tables all willy nilly which should upset some of the patrons who will in turn start fighting each other. Once one of you has the shard, you could leave the tavern during the commotion. The rest of you, who at that point might be interested in the shard, follows. I would take an alley to avoid prying eyes. Then we can enter he next scene. 

This is up to you guys of course. It's just a few ideas and hints. Ultimately how you take on this situation and the story is up to you. Just know...you ALL want that shard. It's the key to the adventure.