Restoring Nexus S to factory everything I'm running a Nexus S i9020A on CM9 ICS 4.0.3, with a Matrix 1.46. I've found this website which seems to contain a fastboot image. I was wondering if I use the fast boot image on my Nexus S. Would this keep or get rid of my Matrix Kernal (I would like to get rid of it), and it would unroot my phone right? 

Basically, if I use this fastboot image on my Nexus S will my phone be exactly like it was, just on 4.0.4?
As long as you reflash both the boot partition and the system partition it will take you back to a stock version of Android. The kernel is packed in the boot image, so that will overwrite a custom one, but a system image alone will not.

You could also choose to flash back to a stock recovery, but that has no real bearing on the Android system itself and custom recoveries are much more robust, so I would personally not recommend reflashing recovery.