Couple of thoughts:
Even if you get a 5.7 or a 7.62 Tokarev that can go through body armor, by the time they penetrate the armor they are only good for maybe 5 inches of ballistic gel penetration. So if the round penetrates the vest, but hits a rib or the sternum on the other side the round isn't going to stop the bad guy.
If the guy has body armor on, odds are the bad guy also has long guns and you are going to be severely outgunned; as in LCP vs. AR-15 or S&W 642 vs. shotgun?.....no thanks.
When you are are outgunned, distraction is your best hope. Since Aurora I've started carrying a powerful pocket flashlight the idea being I can use the flashlight to blind the BG and maybe get off a couple of good shots.