I do not know the European definition, but where I have operated recently an airport is considered isolated when no practical alternate exists. So it would depend on the fuel and ETOPS capability of the airplane in question. Operators should have an isolated airport policy regarding weather and fuel reserves e.g. 120 minutes fuel at the cruise rate instead of fuel to an alternate could be acceptable, but only combined with a good forecast and a PNR by which time a weather update is received to ensure that the flight has a good chance of landing. Then you have to consider the risks if the isolated airport only has a single runway - in itself not a risk if no other airplane is arriving there before you but after your PNR. but one to consider if you have passed PNR and cowboy airways go in ahead of you and do a wheels up landing. All has to be agreed with the certifying authority of course.