Well, Allyson Felix technically hadn't competed in the Olympics yet, at the time, but she forfeit her collegiate eligibility, to get paid by Adidas, because she knew that's where she was headed.
I don't know about dumping a scholarship, but Shannon Miller and Dominique Dawes both deferred college, until they were older, in order to capitalize on their success. And Kerri Strug was ruled ineligible to compete in collegiate gymnastics, because she did monetize her fame. Gabby Douglas' collegiate status is not known (or else, I'm not looking hard enough), but she definitely competed for money at least once, between the ages of 18 and 22. After London, Aly Raisman enrolled in a college that does not have a gymnastics program, and made no attempt to pursue collegiate eligibility, as she pursued a professional career.
Katie Ledecky comes from family money, and I vaguely recall an interview where she more or less admitted that that was the only reason why she didn't take money.