Again, do you mean the app itself or are you worried about the data within the app? You can easily restore previously purchased apps from the store on the device or iTunes on your computer... but are you worried about data loss within the app(s)?
If you're using iTunes you can Transfer Purchases (on the device menu) from your device to iTunes. After your fresh install you can sync them back to the device. I manage apps from my phone but occasionally update them all in iTunes that way.