Pics at a nighttime outdoor party with large firepit

I'm usually a high ISO (handheld) or low ISO (on a tripod) shooter.  Tonight I'm attending a party with a large fire gonna be roaring up out of a firepit.  The host says "and of course you'll take pics for us, right?"

My first inclination was just to high ISO (D5100 and f/2.8 lens) my way through.  My next thought was to use a Speedlight on-camera, something I rarely do.  Sure it will light up subjects pretty close but it's the whole effect of the fire illuminating the subjects/ambience I'm concerned with.  I really don't like the "flashed" look but maybe it's required tonight.

Your thoughts?  Shoot a little of each?  Mostly ambient but some low flash (problem there is I'm stuck shooting below shutter 1/200.  All ambient?  Too slow a shutter the entire party will be blurry.  I don't want to be on a tripod, that would look just too serious and I want to kind of disappear on the sidelines.