I know a lot of young people that are leaving megachurches for more conservative denominational churches because they like the tradition.
Most young people do like modern praise and worship, but many also like traditional music (I am surprised at how many since I thought I was in the minority by far here), which they don't get very much in megachurches.
Evangelical seminaries are bursting at the seams. They can't add faculty to keep up with the boom.
No doubt in my mind that most young people reared in churches leave. But those who are staying are serious about their Christianity in a way that some previous generations weren't.