Huge, huge mistake.
When I tried "returning" I was either too corporate for startups and too startup-y for large organizations. I was both too young for roles I had already filled and too old for technical roles I was interested in.
I bounced through a series of startups, averaging less than a year before leaving.
I tried consulting but could never command the rates that would make it worthwhile.
I tried my hand at my own startup and failed miserably. I did not have the business sense, could not find a partner, and failed to convince a single investor to invest.
I suck at business and organizational politics.
I fell into the role I had in the 1990s which gave me some brief status and minor wealth, but was too busy firefighting then to learn how to leverage that into a better role.
While I believe I excel at managing stuff: people, projects, technology, it is hard to convey that in an interview.
Eventually I said fuck it.
I stopped applying for the CTO and I/T management roles I was interested in.
I told recruiters I am retired, but this had adverse side-effects I did not expect. I now reply that I am not interested in whatever role they are offering this week.
I used the knowledge and experience I have to switch to investing full time, now about a 50-50 mix of publicly traded stocks and startups in various stages of success/failure.
I mentor students in local bootcamps and try to help them find jobs after graduation.
I am still deeply technical, I throw together mock services and run them on different platforms to see what works, what fails and use that to guide my investments. I play with things like containers and IoT crap at home to keep current.
I hang out here to learn what the new hotness is (both what HN thinks it is, and what is coming in from the edges).
I learn a lot from the great writers here like patio11 and tptacek and others.
What startups have up and coming personnel to track? Which startups have people to avoid? I definitely check out founders and lead technical staff of the startups I invest in. If someone is a jerk here, they are unlikely to be someone I want to invest in.
I do not know if any of this counts as "leaving I/T" or not.