Whoever represents a country is whoever has military control over the land and population inhabiting that country. Very rarely is there any other option (e.g. exiled leader).
Belgium in WW1, France and Greece during WW2, Spain during Franco, and I’m sure there are others… It isn’t that uncommon. I’m not suggesting the UN occupies Gaza permanently, but Gazans should be able to decide who represents them (and I sure hope it isn’t Hamas).