so if you were only running 7 out of 8 cylinders what kind of damage would it cause and how long would it take to do the damage?

Well, first of all the fuel would wash oil off the cylinder, and second, why wouldnt you just fix the problem. Most likely it is cheap and unless you have no compression in that cylinder, its probably also an easy fix. Check for spark on that cylinder and if thats not it leak it down and go from there.

If you can keep the gas out of it you could run for a long time. If it's injected unplug the power to the injector. You are SOL with a carb though. If you are running a carb you should fix it right away...you will fill your oil with gas and destroy your main bearings.