PowerPoint/Microsoft Office, and which version you have, there will be an auto-save every fifteen minutes or so. You can easily check.
For instance, in PowerPoint 2007 Click the Microsoft Office Button, and then click 'PowerPoint Options'.
Look at the 'Save AutoRecover information every x minutes' check box.
In the minutes list you'll see how often the program is set to save your data and the program state.
Unfortunately, if you can only see an incomplete file in your saved location it's not looking good.