I agree with Mullet. Go with the 410/.22 . The .22 is cheaper, and I have never found the 22 mag to be too superior to the standard .22. I have recovered .22 mag hollow point bullets, from backstops, and they did not expand at all. Where as the soft lead of the .22 rounds, all expanded. Yes you can shoot slugs out of a full choke. I used to have a single shot 410 with a full choke. I have shot slugs out of it when I was a young kid. Used to take it deer hunting with my father, till I was able to get an Ithaca model 37 12 gauge, and a thirty thirty. I think it is either Rossi, or Tarus, that makes a short single shot gun, in multiple calibers, and gauges. You could carry an extra barrel in .22, .223, .308, or 410, 20, or 12 gauge. But the .22 is surprisingly adaptable, and capable, to many situations. Again shot placement is key. As for killing a bear with one, is definitely not my first choice of tool for that, but if the opportunity, arises for a head shot, in and around between the eyes, or in the ear, not the fat, and muscle around side of the head, the .22 will penetrate to the brain. We used to have a meat market not too far from where I lived, when I was a young kid, and they would slaughter beef there, and they used a .22 short, to kill the cattle. Shot between the eyes, and it dropped like rock. The .22 410 combo is great, because of the amount of ammo you can carry. Also it is good for flying birds. I personally would rather have a 20 gauge 22 combo, because of the larger slug, and availability of 20, and the variety of shot size, vs 410 gauge. I would choose the sabot slug, as it does have much more penetration.
But all of this is just my opinion. You have the .22 ammo, you just need to decide on which gauge you want. Not a difficult decision. What are you comfortable with?
Wayne