As has been said multiple times on this thread, a true combat handgun ( not a SHTF/zombie handgun) is a open carry firearm used for fighting your way back to a rifle. If you happen to have one on you that is issued, you will have, at maximum, probably 45-60 rounds before you run dry. Hypothetically, you just need a gun that can shoot that number of rounds at a time, reliably, accurately and safely.
If you actually shoot that many rounds in anger and run dry and cannot get to a heavier platform, you are probably being over-runned and the S just HTF!
My choice is Glock but the new 320 has great promise. However, I'll take a Hi Point if that's all that's available.
Although I would be very wary of any MIL that issues Hi Points as a standard handgun! LOL!