Another i7-4930MX owner here, also lost a cap when cleaning thermal paste off. I haven't booted yet, but I'm glad to hear my initial suspicion (that it was just an extra filtering cap) might be right. I hate these tiny SMD components, I can't even figure out where it went!
Looking at it under the microscope, it *almost* looks like it's a bad solder joint? Could the ArctiClean have *dissolved* the cap?
Lemme see if I can post the microscope pics.
I'm having trouble uploading the pics due to the size restrictions, so I'll only upload one of the microscope pics.