Do you think the rest of the world will want to look more deeply into it if he just says “they’ve been relocated, no I won’t tell you to where”?

Well, I do suspect the EU will be more than a little miffed about it. Not enough to come to blows, but probably enough to sanction Israel. That said, that is secondary to the real problem with Trump’s plan: There’s no way the Arab states will agree to this. Assuming he does start exterminating Gazans they’ll flee to Israel, Jordan and Egypt, and while the IDF will be able to keep them from from crossing the border (mostly by killing everything that moves), it’s impossible to expect that of Egyptian and Jordanian soldiers. Gazans will cross over into these two countries, which will lead to a collapse of the peace treaties between them and Israel. Also on the home front, the outrage at all this just might be the last straw that gets an Arab head of state assassinated or lead to some kind of regime change. The former has precedent; this is what got Anwar El-Sadat. Now there’s a very real chance that Egypt, Syria and/or Jordan declare war over this, but even if they don’t this will isolate Israel in the region in a way it hasn’t been in decades. Even if Trump is okay with that, the Israeli government sure as hell isn’t. That’s what will ultimately throw a wrench into the whole thing.