Where will all the people live in the interim, possibly many years?
I cannot speak to fires of that intensity, but I know about extreme flood disasters.
When Hurricane Katrina devastated New Orleans and vicinity (end of September, 2005), it took us 14 months to rebuild and our house was only flooded to a depth of 2 feet. We had no lasting structural damage, but because the water stayed for 3 weeks, all the in-wall insulation was ruined by capillary action to about 8 feet. I.e. the whole downstairs wall. Had to fight the insurance companies on that one because normally they only go up as high as twice the flood depth, 4 feet for our area. Electrical sockets along a wall, by building code, are at 2 feet height so they needed to be inspected and, in a few cases, replaced. The A/C units on short pallets in the side yard were messed up and eventually replaced. Basically, we had the outer walls and all of the wood studs but none of the interior walls. You could stand in one corner of downstairs and see the diagonally opposite corner through the studs. Our contractor checked the studs and supports and verified that they were OK.
When Katrina hit, I was told to relocate temporarily to Ft. Worth, Texas, where I stayed for another 7+ months. However, after the first month, my dear wife and my mother-in-law went back to New Orleans and lived with her mother, whose house had sustained minimal damage. (It was on 3-foot concrete blocks so no rising water intrusion.) When I got back from Ft. Worth, I stayed with them for another 7 months. I worked to earn the money, she worked with the contractors fixing the house.
The bigger picture in New Orleans was that some of the hardest hit areas were also the poorest - an area we called the "Lower 9th Ward." The poverty in that area prevented a lot of them from rebuilding but a topographic reality also set in - that area was a bit lower than some areas, so they had worse damage. One of our computer night operations persons told me that she was in water up to her knees on the 2nd floor of her daughter's house and watched as her own house floated down the street. No power for a few months in some areas, so rebuilding was a lost cause until the utility companies worked through the lines. The Lower 9th Ward was, of course, the farthest from the power distribution sub-stations so took the longest for the lines to be restored.
Literally thousands of residents moved to other cities in a mass exodus. We had a plan called "contraflow" set up where, to get out of New Orleans in the weekend when the storm was coming, the Interstate Highway was made to have both sides of the highways as outbound lanes for about 70 miles. By that distance, folks started to branch off and normal flow was allowed again. Houston and Dallas got a bunch of evacuees. Memphis and Jackson (Mississippi) took in a few. Some areas in Alabama took in a few. They moved to be with distant family and never came back. I remember many cities asking New Orleans to take back their people because their new residents were all poor and were straining their own disaster relief plans. Our mayor at the time, Ray Nagin, was quite vocal in telling them that if they came back they would have no place to live and no sources of food, clean water, or medicine. He used quite colorful language to explain why they couldn't return. He was so "eloquent" that it made the national news at the time.
After the immediate crisis was over and the flood waters were finally gone, huge parts of the city were like ghost towns. The few restaurants that managed to open after about three months were deluged with customers who were tired of sandwiches and cold meals. I could come home once per month for a weekend visit. About five months after the flooding was down, we went to a Chinese buffet and, where we parked, we could see the pile of cardboard food boxes they were emptying. Both of their dumpsters were overflowing and the pile of boxes behind them reached six or seven feet high. It was like that for every establishment that could open. The local news organizations interviewed some of the workers, who admitted that they felt good about feeding so many people, but that when they went home at night, they felt physically drained from the volume of customers.
The stores that sold building supplies were also really busy scenes. My wife talked to someone in customer service when she was applying for a store credit card. That person said they had 17 tractor-trailer rigs come in each morning at 5 AM to unload. By sundown, whatever they had brought it was sold, almost completely gone. It took us so long to get our house back together because one of the things in greatest demand was dry-wall (a.k.a. sheet rock). Plywood, particle board, dry-wall, and lumber in general had to be trucked in because the local factories that would have made those things closer to home had also been flooded. I remember reading that people in Wyoming and Montana were complaining about scarcity of building materials in 2006, but we were soaking that up as fast as the stores could bring it.
Now, just short of 20 years later, there are still areas in parts of New Orleans that look like a disaster zone. For us, the infrastructure problem was that flood waters softened the ground and pretty much killed the road foundations. I expect that for Los Angeles, their problems will be whether they had above-ground utilities in particular areas, because if they did, the utility poles will have to be replaced first and roads will have to be tested for concrete spallation. Concrete under extreme heat expands unevenly, causing cracks. And of course, if the road was asphalt, the question would be "how much of it burned away?"