I would say that probably as much as 50-60% of Egypt's population would be gone if the Aswan dams were hit with a nuke (there are two dams, the earlier British Empire one built in the late 1800s or early 1990s I think and the larger one built in the 1950-60s with Soviet funding that is some distance from the British damn). The vast majority of the population live right on the riverside with most of those population centres downriver from the dams. Some of the cities are sufficiently spread out that any flood waters would have minor impact on the outer reaches (I've spent a lot of time looking at Google Earth
)
You have to consider too, that something like 80-90% of Egypt's agriculture is on the banks of the Nile, once its fertile soil is washed away it will not be until the next inundation of the Nile before fertile soil is again deposited along the river plain (actually it would probably take a few inundations and they only occur once a year). The rest of the country, aside from an oasis here and there, is very barren with little to no chance of finding any plantlife let alone any animals for food.
As for the Suez Canal, with it gone, the major source of revenue for the Egyptian government is lost (trying to recall what someone I know said about it, apparently the Suez is the biggest income earner with some coal and gas in the Sinai as second and tourism is third or fourth but these figures come from the late 1990s-early 2000s)
So, no money and no food - I think there would be a lot of desperate Egyptians loading up there trucks and driving to Israel and Jordan (they don't much like the Libyans or the Saudis apparently so they might not try to survive that length of travel) and those in Alexandria would possibly try for Crete or Cyprus (I tend to think Port Said on the Suez would be a target for at least one warhead).