Keynote crashed, presentation file disappeared

In searching through the discussion forums, I've found a lot of disastrous problems that people have had with Keynote, but not this exact disaster.

I'm running Keynote '09 version 5.3, on OS 10.8.4. Today, about half an hour before an important presentation at work, I was running my presentation as a slide show, just to make sure all the slides seemed to be working okay. During the slide show, Keynote hung for a while, and then suddenly quit, leaving me looking at my desktop, with no other error message. I went to reopen the presentation, but the file was gone. It had simply vanished from the folder where it used to be. It's not in the Trash, nor is it anywhere else on my Mac, according to the file search that I ran. In Keynote, when I pull down the File -> Open Recent menu, the disappeared file does not appear in the list of recent files. If I pull down Apple -> Recent Items. I can see the disappeared file in the list of recent documents, but then if I try to select the file, nothing happens.

So here are my questions:

1. Can I recover my file? I've already had to cancel my presentation today, and I would be able recreate my .key file by going back to an older version and redoing three or four hours of work. But I'd prefer not to redo that work, if I can help it.

2. Is it safe for me to run Keynote? Is it going to continue destroying every presentation file that I open?

3. Is there some larger problem happening with my filesystem? Is it safe for me to run anything?