If an airfield is officially closed, its existance ceased - there is no longer any landing site. You could do a safety landing though, and if you find out after a thorough inspection everything is alright and the engine had some kind of morning sickness sticky valve, you just take off again. No permission needed, neither landing nor take off. By good airmenship safety landings cost no landing fee either. Be prepared to discuss in case of an investigation, but all due to flight safety.
But, if you know in advance by NOTAM or other, simply don't go there.