Would my monobrow (unibrow) grow back thicker if I cut it with a pair of scissors and not shave it?

No. If one could make hair grow back thicker by shaving, i'd be shaving my head twice a day. You'd do well to have an aesthetically oriented plucking regime: never move the inner end of the eyebrow outside of a vertical line thru the inner corner of the eye. Don't thin the height too much. There's alot more to it. In my opinion, it's most often done wrong especially if waxed. Male brow should be lower.