I had similar questions about 6 years ago when I first got started.
I had earned two master's degrees in different subjects, worked for various companies, and then I wanted to teach, so I earned a PhD from one of the world's top universities (I'm not kidding). I thought being a professor would allow me the autonomy I sought, not to mention long holidays where I could spend my time researching and writing.
After two years of that, I'd had enough...politics, never-ending pressures to generate original research, plus a heavy teaching schedule had made me a very unhappy person. I've published a book with an academic press (a revision of my dissertation), written academic journal articles and chapters in books, done numerous conferences, supervised postgraduate theses, etc...so I was full-on.
I'm not sure how much you know about working in higher education, but the fact that I got a job immediately after graduating is, itself, pretty amazing...many academics cannot find work, so they adjunct (teach a class here and there) and get some other low-paying job that gives them benefits, and try to scrape together a living. So leaving my job looked absolutely insane to most of my colleagues.
Anyway, now, I'm making 4x what I made as a prof and I get to work from my home office, take time off when I want, spend time with my kids and wife...it is pretty great. I've not always made what I make today, but I've never made less than what I used to make. I do work longer hours now, I believe, so it isn't a 4 hour workweek by any means, but I'm working on that.
That said, I miss the camaraderie of the academy. I deeply enjoyed those times when I could grab a coffee and chat about some esoteric topic with a colleague who is equally keen on the subject. It isn't a bad life, but I did the 'corner office test' one day and asked myself if I'd want to have the dean's life in ten years. I didn't feel that was the life I wanted to aspire to.
Working in IM can be lonely, but I'm fortunate to have some good friends and a great family. For everything I've given up, I've gained in other ways, so I try to remain grateful.
As for crisis plans, well, life itself is uncertain, and things happen regardless of what one does for a living. Still, I try to save aggressively, having the equivalent of a year's salary in the bank allows me to sleep at night. Also, once you get into a cash-generating business, it can be a stepping stone into something on a larger scale. For instance, I could buy/renovate property right now. I could get into SaaS. I could buy an existing business with a proven cashflow, grow it for a year, then resell for a profit, etc.
With anything you do, there should always be a Plan B, C, D. Once you find some success, save, reinvest in the business, then work on diversifying.
