I have an old Husky small ring rifle that was buggered up the same way. I should have tried out the "gunsmith" with a less risky project before trusting that to him (better yet-find a better 'smith). However, once it's done, it's done.
You will get different opinions on your question (natuarally)
. Some will say that an expert can do it without problem. Others will look at you like you're crazy to suggest welding on the receiver ring of any rifle. The problem will be finding someone with credientials, that will actually do the work and stand accountable for the results. It probably can be done, but you will want to be VERY picky about allowing someone to weld on the receiver ring of a rifle you intend to shoot. If it's a run-of-the mill WWII Mauser, it's probably not worth the risk and money. If it's anything special, that may be a different deal.
Sometimes the old holes can be plugged, epoxied, and peened, so that the flaw is almost invisible. Then new holes can be drilled and tapped correctly. I think that is the most logical way to procede, although I have not done anything about my problem rifle yet either. I have seen some that actually look pretty good and since in reality the mounts will cover the screw-up anyway.......
The bottom line is probably "the bottom line". Is the rifle worth the trouble? Only you know that.
You may hear from someone on here that has the perfect solution. If so, I want to talk to him also! Good luck!