if you are not in a hurry which i personally would advise you not to rush into it, and if circumstances allow, try consulting your country's oral maxillofacial surgeon. go through some online medical journal or research if you can. that would be the best way to understand what all these procedures mean and how it would impact you. one would really need to have a very compelling reason to do it, and doing the surgery should give you an enhancement or better your life, and if it does, then it would be worth doing. if the pro is not a major trade off for you, or the con outweighs the pro by a far distance, you might want to reconsider and seek other alternatives for your initial reason for considering cheekbone reduction.
usually a lot of cases for zygoma are really really wide bone structured patients who did it, and apart from the width or dimension of their bone structure, thickness of the bone would likely be taken into consideration. the amount removed basically would mean that the area would be empty right? as much as your skin is attached to the facial muscle or should follow your bone positioning, it would not be able to fill up or stick to the new position completely. this would mean if you happen to remove a lot, then you would definitely need to find ways to eventually lift the skin to the new position. of course, this is my layman understanding and rough explanation of how this should works. and also, if is not highlighted enough, when it comes to any facial contouring, your age when you get the surgery done matters a lot. your lifestyle and how active you are would likely come into play to how your skin laxity would be too.
my genuine advice for anyone who happen to be reading this, you need to have some understanding on these surgeries. so that when you discuss or ask your surgeon questions, you are able to understand their surgical plan better. i think it also serve as a gauge if you and the clinic are on the same page, from both expectation in terms of results, and also their surgical methods (if you done your research enough to know) if it made sense to you. trust me, this should help you filter out certain surgeons or clinic too.