I once put my favorite rangefinder lens in my coat pocket in the desert…then picked up rocks and put them in the same pocket… The lens was toast. Your's looks much better than mine did!
I used to tear-up my rear elements with my wide MF lenses regularly and then it was simply a matter of sending them in for repair, wait a few weeks for a new element to be shipped from Japan and then I'd be as good as new. It may be worth calling Olympus to see what they think. Some of the big telephotos from N & C are designed for quick and easy replacement, though I don't know about the cost.
I'd say keep using it until you find an issue.
One person told me years ago in the days of film that putting a little matt black paint in a lens gouge may help reduce issues with flare.
To the contrary about stopping down, that may make the spot more distinct, especially when you shoot closely.
I would say before you do anything else, go out and do some testing--shoot at different focal lengths and different apertures at each length then take a look at the files. Try the lens toward the sun, away from the sun, shoot the sky, shoot the landscape, shoot what you normally shoot.
If you don't see problems with the files, then you are OK. If you find certain situations that show the scratch, then you may have a problem you can deal with.
