Are people who left academia happy with their decision? Is there any extensive research/study/survey that looked at what percentage of people who left academia were happy with their decision after X years?

I mostly interested in the computer science field (machine learning) in the US, but curious about other fields and locations as well.

People leaving academia can be PhD students or after (tenure-track, tenured, soft-money research positions, national lab researchers, etc.).
I believe some of the national longitudinal surveys would cover this for the US. 

For instance, the National Longitudinal Survey of Youth 1979 cohort started tracking "middle school" age students in 1979 and is still tracking them. They have hundreds to thousands of attributes including education and many measures of health and happiness (though not all are updated every year). 

Another example is the National Longitudinal Study of Adolescent to Adult Health (Add Health).