In my opinion, almost all of that 50% (that drop out) could program, to some extent, if sufficiently motivated.
A great deal of Computer Science students (half? more than half?) love programming and hit a wall when they come to the theoretical side of computer science. Many of them force themselves through it, graduate, and become successful programmers. Many switch majors to Information Technology, and for better or for worse will end up doing mostly system administration work for their career. Some switch majors entirely, and become engineers. I actually think we do ourselves a disservice by failing to segment Computer Science from Software Engineering; a distinction made at very few institutions, and when made, often to the detriment of Software Engineers, regrettably.
So to answer your question; of the 50% that drop out, I think most end up as sub-par programmers, but 80% of that 50% "have programming gear", to the extent that such a thing exists.
People on this board have talked about programming as a gear in your brain that, to a first approximation, you have or you don't. I'm wondering if there's some well put-together resource you can direct someone with zero experience and just a web-browser to and say "if you're having fun an hour from now, you have the gear, good luck" -- maybe something on Khan academy?
(I learned to program a long time ago, and I started with BASIC program listings in my math textbook -- I don't actually know what the optimal onramps are now.)