Yes, a gunsmith could figure it out with a chamber casting, or probably a couple other ways. Krags come in about 3 flavors (if memory serves)--US, Danish, and Norwegian.
Original calibers were .30-40 Krag in the US, an 8x something or other Rimmed in the Danish, and 6.5x55 Swede in the Norwegian Krags. Most common you'll see here are US Krags, and few get modified from the original calibers. I have heard of some being converted to .444 Marlin, because it just barely fits inside the magazine assembly (with a little bit of opening up). I'm still kicking myself for passing up on the Norwegian Krag I didn't buy years ago (no stock, all metal present, but had been sporterized). A Krag of some variety (preferrably unchopped) is still on my list of "to gets."
As far as worth, that is dependant on condition, whether it could be returned to original configuration, is it an heirloom, etc.? Sight unseen for a sporterized US Krag in .30-40, maybe worth about $300-450ish to the right person. If I'm totally off, someone will come in and correct me I'm sure.