NATO would not be able to shield him from any sudden accidental tragedy that could befall him!
As for the UN being kicked out of NYC ---
The headquarters of the United Nations (UN) is on 17 to 18 acres of grounds in the Turtle Bay neighborhood of Midtown Manhattan in New York City. It borders First Avenue to the west, 42nd Street to the south, 48th Street to the north, and the East River to the east.
Prime real estate, for sure.
Trump has his eye on it, for Trump EastCity.
POTUS
could kick the UN Headquarters out of New York, by "simply" unilaterally withdrawing the US from any and all United Nations memberships and treaties -- at which point the US would no longer be bound by the UN H-Q agreement and could tell them to piss off.
What would be more likely to happen in practice would be that the US would formally ask the UN to move their headquarters elsewhere, and the UN would probably answer "Sure, just as soon as we agree on another country/city to host the HQ and finish building it" which would probably take quite a while...