They can really ask this question two different ways.
1)What would you pursue if you couldn't do dentistry?
2) What would you do if you did not get accepted this cycle?
I think they ask question number 1 to try to understand what other interests you may have. For me, I would pursue a PhD program so I could teach at a university and do research. Your answer could be dramatically different than mine.
For question 2, I think the responsible thing and best answer is to say you would double down and apply again.
In the long run dentistry will beat nearly all of these opportunities. If you can find a job that makes 80K plus with good job security and the potential to grow to 140K after a 20 year career (which would probably end up being 175-200K when you consider inflation over the next 20 years) then maybe you should snag that opportunity. The quick ticket to middle class america, however, is only getting rarer and rarer and dentistry is one of the finest ways to become more than financially stable, well educated, and a future community leader. I'm pretty sure if you dig in now and become a dentist both you and your wife will be thankful you did in a decade from now. Don't get discouraged when you're so close to the finish line! Did you do poorly on the DAT, have a weak GPA? What's making you second guess yourself? Have confidence, own your interviews, and look forward to starting next fall.
Also, you can always work while you're applying to dental schools to alleviate some/all of the immediate financial strains.