I am planning to update my iPad to iOS6 but iTunes says that all or some files might be deleted like apps, music, or photos.

So I searched something about this matter, and I found out that I can backup all the apps I downloaded. I tried to backup the apps, but some of the apps are only backed up -- those which are downloaded by my e-mail account. Applications that were not backed up are those apps that were downloaded by another e-mail accounts logged in at the App Store.

I also tried to search on that matter, but no right search results were given.


So the question is, if I tried to update my iPad to iOS6, will those apps that were not backed up or apps that were downloaded by another account deleted? If it will be deleted, is there any way to back up those apps?