Speaking as a Mormon (LDS), and a member of my ward's (congregation's) "Building Maintenance and Security Team", we don't have a specific plan (I am aware of) for dealing with such things as an armed attacker in our meetings. However, when our team was first organized last year (replacing the previous "Building Committee"), our Bishop brought up the subject of carry at church during casual conversation. I and one other member of our 3-man team carry on a regular basis, and we both interpreted the Bishop's comments as sort of a "wink, wink" encouragement to carry at church. (I have carried concealed there using that and personal self defense as my "good and sufficient reason", especially after a Bishop was shot and killed at church last August in California.)
At church meetings, I keep to CC, but one of my other responsibilities is to check the building three nights a week (making sure it is locked and properly cleaned/taken care of after scheduled activities). When I go to perform those checks, I am always armed, and (unless the building is still in use) OCing. Hope that helps a bit.