Twice I've had large pigs come up to the edge of the pen when I was inside filling feeders, they weren't scared at all. Only had snake shot loaded 9mm one time, he eventually went back in the brush. The other time was at my pig setup with 2 holes cut out of the bottom of the panels. That one is a very small (4 panel) pen and I admit I was puckering a little!

should have shot him in the eye

I think you've come to the wrong place if you want to be talked out of "needing" another gun.

I would not carry rat shot unless I was carrying it in a spare mag for snakes. You may look into some hard cast +P ammo like the stuff offered by Buffalo Bore, that should work very well for most swine issues. Also, consider some of the stuff from Lehigh, they have some "extreme penetrator" though I have never used it. I carry a Glock 21 in the woods with my duty ammo (230 grain Ranger SXT +P) unless I'm in bear country then its my Smith 69 in 44 mag. The main thing is carry what makes you comfortable. If you shoot a hog, maybe use it for a crash test dummy and shoot it at different angles with your 9mm and see how well it penetrates and if you are happy with the results. That should give you peace of mind or make you switch, depending on the results.