So I put myself through the game and came out dumbfounded like practically everyone else. I read up some theories and gave everything some more thought, and this is what I came up: (I know that Kan already revealed that there's not a true meaning and it's all open to interpretation, but I'd like to write a little about it anyways.)
I came up with two major theories. By now we're probably all familiar with the "61|5491" code hidden in the game. It's generally believed to refer to 7/16/1945, the day of the detonation of Trinity-the first nuclear bomb. And thus people have speculated that "birdy" represents the A-bomb/the warplane carrying it, therefore "birdy is over Europe", the disappearing nations on the map...
I did some more research. The fire take splace at 3:26, when the final switch is thrown. I believe it references March 26th, 1954, the date of the first detonation of a Hydrogen/Thermonuclear bomb(I haven't seen anyone talk about this at all...). This, along with 61|5491, is probably enough to confirm that there's definitely something going on here involving the A-bomb.
So how does the bomb tie in to everything? I believe that Leah represents humanity-as a whole. And "birdie", war, or the incentives to instigate war. This is why Leah is faceless-she was never supposed to be an individual with unique and defining features. The fire is supposed to be the aftermath of the Hydrogen Bomb. Humanity "slept it off" and ignored the issue. The critical thing to understand here is that the first H-bomb was several hundreds of times more powerful than the first Nuclear Bomb-truly able to wipe out the world. And that's precisely what happens.
The map. I've noticed that China, the USSR/Russia, and the USA disappear first. It'd make sense that they'd be the first nations to be annihilated in a global atomic war, due to political and tacticla reasons. And the last patches on the map to remain are central African nations, generally considered politically obsolete. Instead of nations being lost to the bombs, however, the map could also signal the sequence in which the nations receive nuclear weapons. Historically the USA, China, and the USSR were the first to have nuclear capabilities. And it makes sense that lesser nations due to technological issues and weak economic abilities would get them last. The bronze globe had an odor coming off of it. That's to say that humanity is rotten, or Earth is sick with radioactive fallout.
There's also the microscope and the liquid sample. The cells we see start out looking normal enough. But with time they turn dark and sickly and appear shriveled up. That's to represent genetic mutation due to radiation. And finally, the cells disappear...
The ending? To be honest, this theory doesn't quite explain it either. She shot something-the gun was clearly not pointed at herself nor birdie, but down-and disappeared. So did birdie. All I could some up with is that she shot the world. Literally. Humanity wiped itself out with the bombs, and war naturally died as well. Or, alternatively, she emptied the gun-humanity dearming the nuclear bombs. Birdie no longer carried her because war no longer had a grip over humans, who after all the destruction and bloodshed finally came to their senses and made peace.
There is also this other theory that I came up with. The picture of the cells used is thta of the real-life bird flu. It could mean that instead of nuclear apocalypse the world is threatened by an epidemic. Thus, birdie would be the flu, whose being over Europe would mean that it's infected the continent. Leah would then be a scientist who's desperate for the cure. I theorize that she's an adult, but sees herself as a child because of all the death and destruction around her. Children were blissfully oblivious to many matters and being younger was a desperate means by which she attempted to cope with the world's end. But in the end I prefer the A-bomb theory, since those dates and times being there is pretty much undeniably referencing the nuclear bomb. At the same time though, the usage of the bird flu image could not have been a coincidence-Kan checks his image sources.
Again, all open to interpretation, as the man himself said, but this is what I believe, any thoughts?