If you are talking about the four securing points on the sides of the lcd it should be fine with out one. If you are really wanting to try to patch it I wouldn't really recommending gluing it. Just secure the other three.

I just had a similar issue on an iphone 5s that wasn't recording sound or allowing the other caller to hear them. Nothing physically wrong with the lighting port which controls this mic but removed and replaced with a new port and it is working clear as day.

I have to concur with Ethan on this one on having to at least by replacement glass. Although I have done a few of these core Primes with no damage to the lce as they are not laminated together.