You must come from the UK with a DVLA. In the United States, until recently, diabetes meant revocation of both a CDL (commercial driver's license) and pilots license. Modern changes in the law permit retention of the CDL if special monitoring is done, as well as permitting private pilots with diabetes to fly if they closely watch their sugars. That being said it is unusual for someone with diabetes and high blood sugars to "black out". Usually that is the case with low blood sugars. Sometimes people black out for reasons that can never be determined. It happens once and then never again. I am not satisfied that the blood sugar levels are the cause of your momentary loss of consciousness. You need to get a test called an hba1c. In the United States many people with diabetes simply fib to the motor vehicles department and get a fly-by-night physician to sign their six month physical. Be very careful what you put down on the form you submit to the DMV. I am not telling you to lie, but a single episode of syncope may not be something you want to bring to their attention. Sometimes dehydration or illness can cause such a problem. Syncope is not a diagnosis. The term says nothing whatsoever concerning the etiology of the medical problem. Presumably you had both an MRA and an MRI. Right now be very careful. If the black-out came from a form of epilepsy there will usually be an "aura" or sensation (sometimes on the tongue) a short while before the event. If you feel something coming on do not hesitate to pull to the side of the road and stop immediately.
Syncope is basically another word for fainting.
If it was because of high sugar levels...then no...they shouldn't revoke it.
Unless it's because you are diabetic and NOT making an effort to control it...in which case they could, but I've never seen them do it before.