If it's all you have, goes bang, and spits out lead the .22 Mag would be better than a sharp pointy stick.
Around here it's the preferred poachers round for deer.
At 145 yards a plain old Super-X JHP from my Marlin will punch through 1-1/2" of treated lumber I hang my targets on.
A .22 Mag wouldn't be my first choice at all as a PDW, but I'd say we can all agree on one point ... I wouldn't want to be standing in front of one.
In regards to the drug crazed wackos, unless you can put your shots into the cranium or spinal cord its not likely that any handgun round will stop them. It will mortally wound them, but not stop the threat in the immediate miraculous way that HP bullet manufacturers promise.
That depends on too many factors, and many scenarios could play out with a "DCW". Not all drug crazed wackos behave in the miraculous unstoppable way that the TV portrays.