This is what I recommend. Bottom line - be proactive. Do as much as you can do to insure that all of your content is safe and retrievable if something goes wrong.
What you should do anytime that you update the device is to transfer purchases from the iPad into iTunes - File>Transfer Purchases - and you should backup the iPad as well. When you update the update the device, if something goes wrong, you can restore from the backup.
If you have any other important files, you may want to transfer them to your computer as well, prior to the update. If you use file sharing apps, you can transfer the files via file sharing and syncing with iTunes. You can transfer documents using DropBox if You have a DropBox account and the DropBox app.
If you have photos and videos in the camera roll that you do not want to lose, you can import those to your computer as well.
How to backup and restore from a backup
iOS: About File SharingiOS: Importing personal photos and videos from an iOS device to your computer.