If you have had that much trouble, bite the bullet & give out the comps.
I feel it would be a cheap promotional cost.
it is hard enough to build up a bums on seats demographics, so don't loose them for the sake of a a part paper house. It will cost you more in the long run. Rather than just not honouring the contract, implied by the purchase of a ticket for a show that  didn't deliver.
By giving the offer of comps, I have found the punters nearly always bring along others, who pay.
You could do it for a particular designed performance or just make it an open season date [with a sunset clause]. Which in my book the latter is the way to go, rather than offering money back!
Lets face it in most cases, they won't all front up on the same night & a lot will forget about it anyway. There the liability would be spread over a number of seasons & costs little or nothing anyway.

If you have not completed a certain performance of a show you may be able to get an extension of the contract for the uncompleted show. In that case I would suggest you offer that night to your audience. Obviously if you own the performance space this will be much easier than if you are in a rental situation.