They kept the truck running and the barrel rolling which was pulling concrete up on the low side making it worse.  At least the mixer should have been stopped, and better yet reversed a few degrees before stopping it, which would have transferred a lot of weight to the high side.  I also think that pulling it from the front with the tow hook as soon as the wrecker got there might have saved the day because it would have likely pulled the wheels back up onto harder surface.  Of course, it doesn't matter now.