Two things.
I'd sure take some brake pad or carburetor cleaner and a bore brush to that barrel before giving up on it. I can't tell you how many barrels I've "rescued" simply by an aggressive cleaning. I love to follow in the wake of guys who go "natural" in their components and cleaning to "season" their barrels. When I remove all their seasoning, I've got a real shooter at discount prices.
If in fact the rifling is gone and not filled, I'd sure talk to one of the barrel makers about opening that to a smoothbore. In my experience there's a lot to be said for small charges (1/2-3/4 oz) of shot for small game inside 30 yards. That would be an ideal candidate, whether or not you ever shot a patched round ball through it.