Rovaniemi, Finland was burned to the ground in WWII by retreating German forces, although it had been heavily damaged during previous battles. Some of the citizens fled to neutral Sweden, ~120km away, by crossing the river at night, others left for villages and towns where fighting was less heavy. A few remained in the city; German forces originally declared that only public building should be burned, and houses should not be touched, but 90% of the city ended up being leveled.

This fighting took part mostly in the summer and fall, so travel for displaced citizens was easier than it would have been in the Lapland winter.

I'm not a historian. I hope that's okay.

I'm from Hannover, Germany. This is what it looked like after the war. Half of the buildings were destroyed, the inner city was almost completely destroyed.

Casualties were sometimes in the 10s of thousands, but often less. You can find a list of casualties in german cities on german wikipedia. German cities were in general not evacuated, but there was a program for children. During raids, the population would go to the basement. This wasn't completely safe, buildings could collapse and kill everyone there, but it basically worked.

Cities were not nescessarily completely destroyed, the pictures like yours are usually from the inner city. Allied raids made use of landmarks to determine the target. For example, in Hannover, they came in from the south over the Maschsee and drop the bombs behind the lake, in Magdeburg, where i live now, they used the cathedral. This has the effects that on the one side of these landmarks, the cities were hit bad, while on the other side, often a lot of buildings survived.

After the bombings, a lot of people moved to the countryside if they could, but basically people stayed in the cities and started cleaning it up. This was mostly the work of women, called "Trümmerfrauen". The rubble was sometimes used for construction. For example the western tribune of Hannovers football stadium (an older picture before the last modernisation) is made of rubble from the war.

Richard Overy (The Bombing War: Europe 1939–1945, 2013) covers this very well for all the different theaters. For example in the case of Germany, there was a organisation in place, which (provisorily) repaired damaged houses; allocated new homes, furniture and money to people who had been bombed out etc.

Warsaw was 90% destroyed during the war. Of course, most of it wasn't from bombing, but rather from the occupying German Army.

The US flew a number of photographic flights over Warsaw in 1945. You can view these images in two ways.

First, the images were compiled into a realistic 3-d flyover of the destruction. (The details of how this was done are published here.) This flyover was presented in a short film called "The City of Ruins" that was presented at the Warsaw rising museum (http://www.miastoruin.pl/index_en.html). You can see it now on vimeo: https://vimeo.com/16582392

A second way to view these images is through Google Earth. If you install Google Earth's desktop version, you can access historical aerial imagery. They happen to have imagery of Warsaw from both 1935 and 1945. You can really see the before/after of the destruction.

In 1945, the center of the city was mostly destroyed. You can see the shells of buildings, the interior masonry walls of most buildings remain standing, but the wooden roofs are gone, presumably burned.

The northern part of the Ghetto is mostly just wiped away, no sign of buildings whatsoever. A region about 7 city blocks by 5 city blocks is just flat, aside from a single church, St Augustine's. (The church is visible at about 4:30 in the City of Ruins film.) In 1935, that region was packed full of buildings.

About two miles away, across the river, you can see plenty of people. I'm not sure if that was a refugee camp or a market. I've included a screengrab below. http://imgur.com/k68BhQB