There was an interesting article that looked at what the USA Mathematical olympiad trainee candidates in 1980 were doing now (This batch included the famous Noam Elkies) -

http://andrewgelman.com/2015/03/17/1980-math-olympiad-progra...

HN Discussion: https://news.ycombinator.com/item?id=9225683

A bunch of them went into academia, though not necessarily pure math. Some became engineers and only one ended up in finance.