It wasn't even a conquest war. Nasser's re-militarization of the Sinai and the closure of the Straits of Tiran were not preludes to war, but rather an attempt to retain his status as leader of the Pan-Arabist movement. With a significant portion of his army bogged down in Yemen, he wasn't looking for an all-deciding war with Israel.
Yes, gathering 7 divisions (~100k men, 1k tanks, about a third were veterans of the war in Yemen) in the Sinai is just re-militarization. Egypt had 15k-20k men in Yemen at the time. Not to mention that Egypt was not the only one showing up with troops for the coming conflict.
And at any rate, it wouldn't lead to a second holocaust. There would be a hell of a lot of ethnic cleansing as most of the Jews are kicked out of their homes in Israel, and quite a number of massacres, but the Arabs are not going to embark on a holocaust style genocide. Definitely not with the world watching.
No one was thinking that train tracks would be set up, leading to death camps. But it was pretty obviouse that an Arab victory would lead to the deaths of every Israeli who couldn't get out in time. And how can you say it wasn't even about to be a war of conquest, and then that the Israelis that woun't be killed would be exiled?
Two ways to ensure the defeat of Israel.
A. Attack a Soviet vessel, preferably unarmed. Instant Casus belli.
B. US responds to attack on the USS Liberty.
A. In the other thread we went over this. OTL cases of deliberate Israeli attacks on Soviet military units (Rimon 20) have taken place without the USSR invading/nuking Israel.
B. I realy can't see this happening.