A backup is always good, regardless of economic circumstances because you might medical out.

This is somewhat mitigated at majors with good disability plans. If you're climbing the ladder, you're probably young enough to start over. Career changers can go back to what they were doing before if it's not seniority based/age limited. Career pilots who aren't at a top-tier major might really need a backup.

There will of course be a downturn, economies are cyclical by nature. The good news is that airlines are pretty efficient these days, not much fat to trim, and pilot retirements will mitigate or perhaps rule out furloughs at many carriers.

As some have pointed out, a degree alone will not guarantee immediate lucrative employment, especially if the economy is down. But if you don't have specific technical/vocational skills, a degree would be the most versatile backup.

The safest thing would be develop and maintain a skill that you can fall back on. Some things lend themselves to flexible schedules and part-time work, and could be quickly spooled up to full time if needed. (computer programming, nurse, PA, accounting). Many pilots do real estate, that would work if you have a medical issue but probably not if the economy tanks. Also a wide variety of trade/votech skills could serve that purpose, while most pilots would probably prefer white collar work if they couldn't fly, that's your call.