There was a thread on another subforum yesterday that referenced Sheldon Brown's 1/8" rule for chain/sprocket replacement. Of course, I ran out to the garage and measured all my chains, and sure enough, on both of my two recent craigslist purchases, the chains had exceeded the 1/8" stretch threshold that, according to the article, would necessitate replacing not only the chain, but the sprockets/cassette as well.

The two bikes in question are: (1) An early to mid 1970s Raleigh Record, and (2) an early 1990s Bianchi Advantage. Neither has any trouble with shifting or skipping or anything like that, and I don't see any obvious signs of strange wear patterns.

I understand that replacing the chains without replacing the sprockets will probably result in skipping, so I'm reluctant to do that. I'm also reluctant to "fix" something that doesn't act broken.

My questions:

1) What if I don't do anything? I guess, ultimately, the chain breaks, and then I have to deal with it. Does any other bad thing happen?

2) If I were to decide to replace both the chains and the sprockets on one or both bikes, it seems that doing this for the Bianchi is probably straightforward, and I could probably use one of any number of replacement cassettes on the market. (Is that true?)

But what about the Record? Do they make new replacements for the freewheel sprockets for those? Or would it make more sense to think about replacing the whole hub or wheel, while I'm at it? And if I did, would it be possible to fit a new derailleur that would allow me to put a granny sprocket on there?

Any guidance would be really appreciated. Thanks!