If cables can break-in, can they then wear-out?

No they will not wear out if they are not abused or exposed to a detrimental environment. Break in is for real...unless your deaf of course IMHO

Yes.

Nothing lasts forever!

But cables should last a rally long time though. Our ears will probably go up first.

As a former test equipment calibration lab tech, you'd think I felt measurements were everything, but I have seen far too many components (cables included) that measure EXACTLY the same with steady state signals sound vastly different with music.

Now I just repair gear praying I don't change the original equipment sound whilst doing it.

I think we do not yet know WHAT to measure to ensure a particular sound. Years of measuring have given us a pretty close approximation, but something is truly missing in our gear or our approach.