Depends on if I remembered to wear my Wonder Woman bracelets and tiara that day
Anyone with any sense would walk out and call the police. Even if you have a firearm, you have no idea how many burglers there are and what kind of heat they are packing.
I draw my gun and shoot him/her
I would assist the robber. so I can get some monies too :D
I quickly walked back out. (yes, I really did walk in on a armed robbery once)