Hello cjwise5, welcome to DRTV, in a "mega" church, 3000+/- folks,....let's run through some scenarios. There have been church shootings by non-muslims also. Disgruntled folks that want to go down in a blaze of gunfire, taking as many victims as they can and than commit suicide.
OK, if you have a shooter in a mega church, and your armed, the possibility is he may be on the second level, over 100 yds from your position. Hardly in pistol range, (standard carry handgun),.... even at 10- 25 yds, how many panicking folks will be scrambling all over the place, not a good time to take a shot either.
So, unless your Jack Bauer, and going to take the "I'm going to end this" in a mega church, (which will be used against you in court), the alternative is a good defense for you and your family.
Sitting by an exit is good. Getting out quickly is good. Not stopping while you call 911 is good.
However, if your in the middle of the "pack" with a better chance of being trampled than getting low at your seat, making quick looks to see where, how far, what's the BG's weapon,, etc,.. will dictate a different response.
Explosives aside, a crazed madman with an AK, 12g, AR, semi auto pistol and (25) 15 rd magazines, hell bent on shooting everyone, there will be a "space" created that will leave the BG vulnerable to a well placed shot. Most just simply "walk" around shooting. Find a defensive position, column of concrete, wall, threshold, and if you can;t escape, defend yourself.
This is a mega church, not a country church with 30-60 members. That would be a different set of circumstances. If a shooter is across the arena, or on a different level in a mega church? I'm getting my family OUT as a first option.