Zahire Raheem springs to mind....beating Morales and now its like Zahire who?? I reckon Prescot will fall into the same category as that after beating Khan.
Harry Simon. Beat Winky Wright and then disappeared. Not through fault of his own though as he had a car crash. But still.
Disappeared means a single big or elite win then losses/fighting under the radar or no fights at all? Nonito Donaire, (I know I know, but when is he going to fight a live body?), Florente Condes, Medgoen Singsurat, Somsak Sithchatchawal, Carl Thompson, Yanqui Diaz, Shaun George, Carlos Maussa, Corrie Sanders, Ross Puritty, Leon Spinks, Buster Duglas, Kevin McBride... well, if these count, then almost any upset kid can be named who couldn't repeat the success, fighters who could continue winning but with little media attention or fighters who cashed out and left the sport after the big win...