<p>Depends on the college. You'll probably get one or two reminders that you still have to pay the fee but beyond that I am not sure what will happen. Most colleges (especially super-selective ones that already have more worthy applicants than they could admit) will probably consider your application incomplete which would result in an automatic rejection; if a college really wants to have you, they might consider your application anyway (last year there have been a few cases where students were admitted to colleges without submitting teacher recs or essays, and I think one student reported being waitlisted after sending test scores and the school report, even though he never submitted an application (apparently he changed his mind halfway through the application process)).</p>
<p>You could hope that the colleges would consider your application anyway, but it would be fair for you to withdraw your application and save colleges the extra time and effort of processing your application and reminding you of the fee.</p>