This is really down to the difference between education and training.
Education is about the ability to think and understand about a subject, whilst training is about the ability to do something. A degree is an educational qualification, whilst a licence is a training qualification.
So, my degrees in aeronautical engineering are about my ability to think hard about how aeroplanes work. My pilots licences are about my ability to fly an aeroplane well and safely.
It is possible to build on the education that a degree gives you to learn the skills to do a particular job - so in my case, when I first graduated with a degree in engineering, that allowed me to join the graduate training programme of the organisation I went to work for - and a couple of years later, they gave me a real job managing flight trials.
But, if you ONLY have a degree, all you have is a demonstrated ability to think hard about a particular subject: such as engineering, management, environmental science.... Added to a licenced skill - such as a commercial pilot, or as an aircraft design signatory, that can be really useful and help build your career as far as you want to go.
But, the graduate training jobs tend to go to the recent graduates whose "thinking skills" are fresh out of the box, they are unlikely to go to somebody who can't show they've used the education recently.
So, that's why I think that if you want a true backup, get a "licence" - as an accountant, cook, mechanic - whatever you'd enjoy doing and pays the bills. But a degree is something else.
On the other hand, something appropriate to the aviation world: business management, aeronautical engineering, contract law - that degree, added to the existing skill and licence of a pilot, could allow you to grow your career in a different direction (whether you keep your medical or not - after all the skills don't suddenly vanish with your medical). That's almost certainly a good thing, and gives you many more options in your career, but to call it a backup is I think incorrect.
G