Personally I've just finished school, so I'm now going in to optional education (college, then university).
I wouldn't consider not going to either of the two above places. I mean, not only would you miss out on a LOT of education (and qualifications), you're also making friends and creating a backup plan for your life incase your job (whether it's online or not) fails.
MMO for me is just a hobby.. something to do on those boring evenings. I wouldn't want to be sitting infront of a computer screen all day... it'd get so dry!
I didn't drop out of School, but I messed it up big time. Didn't go to classes, took drugs, was always getting suspended etc. You name it, it happened. This resulted in me getting poor grades apart from two (Business Studies and Graphic Design).
Amazingly, this didn't have an affect on getting into College, but it would have an affect on getting a job if I was in a different line of work. As I'm a designer, employers and clients don't care too much about qualifications. As long as my work is top quality, they're happy.
Yes, you might want to drop out and make money online, but it's not easy. There's absolutely no guartentee you're going to make enough money to live off of. So if I could go back and do it again (no matter my future career), I'd make damn sure I could get the best grades possible, and earn money in my spare time. My qualifications would be my fall back plan.