do degrees “expire”?

In certain career fields, you must be licensed and you must maintain your license.  If your license expires, then you cannot work in that field until you renew it.  Maintaining and renewing your license typically requires taking continuing education courses in the profession and/or additional graduate-level course work.  

A lack of work experience could also prevent you from being hired.  It has nothing to do with your degree or how long ago you received it, but rather with the fact that you haven't done anything relevant with it since.

It really depends on the career field.  In medicine, engineering, and computer science (for examples) your knowledge must be up to date.  If your degree is in liberal arts like writing or theater arts, you do not need to be up to date as those particular "technologies" rarely advance.  Which means you can resume or start your career that you intended with your degree after taking time off for a few years or more.

Take me for instance: I graduated with a theater arts degree in the mid-1990s.  After three years of grueling theater stagework, I took about 10 years off and resumed my theater career doing stage construction for a few local companies.

On the opposite side of the spectrum: I knew a college president from a big science/engineering school.  After he retired as president serving 20 years for his school, he wanted to return to teaching engineering classes to undergraduates.  However, he can't since his particular field had advanced too far for him to know anything about it.  And he just simply retired into private life.

Some fields the degree does not "expire," but for other fields it technically does.

decades later, you degree has likely expired.  in licensed professions, if you haven't kept up with continuing education requirements, your opportunity to get a license will likely have expired, and the licensing board may prescribe remedial work to compensate -- perhaps even before you can sit the licensing exam.

Yes.  They all have a secret date code stamped on under the brim that only the manufacturer knows what it means.

That is why doctors, lawyers, nurses, etc. have to pass exams to be licensed to practice, and have to show that their knowledge is up to date. Doctors do constant training on new procedures, equipment, and so on. If you had a medical degree but hadn't been licensed to practice for a while, you'd have to take some very rigorous tests.

You only have to worry if you go into a field of work where all the employers require rigid standards and degrees.  Any education can pay off, as long as you were interested in that field of learning, and you find a company or organization that values your interests and education.

The degree is still a degree. You have it for life. What may expire is your right to practise your profession, like medicine or law, without re-certification. If there is no need for certification it is up to an employer to decide whether or not to employ you.