It all depends on the quality of the sleeve job. It could be a 20% ding in value or it could be a 70% ding in value.

Or, it could even enhance value. A teague lined barrel on a fine damascus gun that was not able to be shot anymore is likely going to increase in value through the barrel lining process. The only question remains: Will the gun increase by <$4000, the cost of new barrel sleeves or liners and reproofing?