Hi, Mohammedm, I know that when you choose to publish to Facebook, you can either choose to publish it as a panoramic JPG which will be embedded in Facebook (and available for you to subsequently save), or share it as an interactive panorama here on the Photosynth site.
Sharing it to Facebook as a JPG is probably the easiest way to obtain a flattened copy.
Since I don't have an iOS device at my disposal, I don't know if the app stores the input photos somewhere on the phone. If it does, however, you could always export them to your computer and stitch them with the panorama stitching software of your choosing.
I wish that I had a better answer than that, but that's about the best I can do for you for now.
Your fellow photosynther,