No, the iPod is designed to mirror your library (or whichever set of playlists or criteria you have chosen to use to sync with) As such, if you delete your entire library it would assume you wanted to do the same thing the next time you synced. Partially this is because otherwise, if you deleted a number of songs, the next time you synced it would have to ask you if you wanted to restore each individual song from your iPod.
The bottom line is that the Apple philosophy is that all your management for your iPod is done in iTunes, you then take the iPod away and use it, when you want to make changes it's done via iTunes. There is a very interesting article at
RoughlyDrafted about how this makes their DRM model much easier to manage and control - although it doesn't make the case as to the relative merits of DRM - that's a different matter.
"Why hasn't the iPod always synced in two directions? Well, the iPod is a dongle; it's ‘iTunes to go.’ As a simple device, the iPod has limited capacity to organize and sort playlists or perform other features of iTunes. The point of the iPod's design is to have all the work done in iTunes, and simply present it on the iPod."
