When Mr House installed the Laser Cannons and shot down the missiles, was going to hit all of Nevada of just Vegas.

And plus if Vegas survived what happened to the people, i would imagine Nellis protecting Vegas but also what happened to the old casino bosses?

And he didn't rescue all of Nevada, just most of the Mojave Desert. 77 nukes were dropped on the area and I believe he disarmed 65.

They collapsed down into tribals like the rest of the world; radiation or not anarchy tends to set back the clock of progress. They may have become the leaders of the tribes but they were still tribals.

He just protected the Mojave/New Vegas, not the entire state of Nevada.

And I suspect like anyone who didn't get somewhere safe enough, they died of either radiation or other people. Vegas wasn't hit like other cities, it's destruction was because of the citizens rioting and tearing things down, etc. I'm sure the casino bosses got either killed or sent out into the wasteland, only to die there.

Anarchy ruled the streets and people diverged into tribes.
Basically, yknow how the Kings control Freeside? Like that, except another gang controlled Westside, another controlled Northside, another controlled Eastside, others fought over the Strip etc and they would all periodically fight with each other. For example, the Omertas used to be at war with the Great Khans, before House reappeared.

Basically I would imagine that with House in a coma, many people dead, radiation an issue and perhaps water aswell (yes Lake Mead is still clean, but without water being pumped, people might not've been aware of this initially), people began to fight over resources and shelter.

Doesnt matter even if all the people in Vegas would have survived, things would still go to [censored] if the rest of the world was [censored]. Vegas is part of the United States. Imagine the United States gone, that doesnt mean the people of Vegas know exactly what to do, even if they all survived.

So Vegas was mostly spared of mutation and radiation.