I don't have supertabs of everyone included, but me and some friends tried to find these percentages once.
Of people I know, or are losely aquinted with, we were about 300 people in my flight school over the time I was there.
Of those about 5% quit training before conversion to JAA.
10% don't finish, or are stalling a lot with their JAA (ATPL) conversion
around 20% have any kind of aviation job. From flight instructing to jets. Maybe less than 5% have anything you would consider a "career making job". Quite a few work in airports, checkin, ground handling, cabin crew. A grand majority have given up and are pursuing different careers.
All in all, it's fun how the flight schools always try to paint a rosy picture, but no one ever tells you the statistics. And every time they say "work in aviation", they also include cabin crew, ground staff, anything close to an airport basically.
I would still do it again, but I would do it with my eyes open.
Anyone who asks me, I give them the true story of it, and many of those reconsider everything.