I carried a 9mm pistol for a while, but a few years ago I swapped it out for a .22 instead. If a hog runs my direction, there's no way I'm going to drop my rifle and grapple for a pistol, and for a finishing shot on a downed hog a .22 is fine. Plus, the ammo is cheaper!
If you're concerned about whether or not a hog is truly dead, poke it in the eye with the tip of your rifle. If it flinches, it gets another bullet.