Will two missing screws on a distributor cap affect running condition?

What happens when distributor cap screws are missing. What problems can it cause to my car is a 97 honda accord.

As long as the cap does not rotate on the body of the distributor the timing will be unaffected. However, if it is loose this will cause the spark to have to jump further across the gap resulting in a misfire.
The worse thing that can happen is that parts will shake loose and the car will completely stop firing. This can result in air/petrol mixture travelling down the exhaust pipe and exploding, making a hole in the silencer (this happened to me once).

If the cap moves it will make the plugs fire out of time and if bad enough the car will not run.
You need to replace the screws.