There has much confusion around unrooting the GSII. Zedomax was kind enough to make a once click unroot for us but there is trouble with it removing the customer kernels that have been included in some of the roms. I have put to together one place where there will be working links for everything that has gone missing. Getting stated there are multiple methods to unroot the phone and bring it back to stock, ODIN and Clockwork MOD recovery
Clockwork Mod Recovery Method:
Step 1. Download these 2 files :::Stock Kernel::::Zedomax's unroot rom::: and put in the root (meaning not in a folder) of the SD card.
Step 2. Boot the phone into recovery mode by hold vol +/- and power once it shows the Samsung logo let go of everything (Or from the power menu if you are using the JUGGERNAUT best rom IMHO).
Step 3. Using volume +/- key highlight "Install Zip from SD card" select it with the POWER key then using the same method select "Choose zip from SD card"
Step 4. Highlight the downloaded file (should be named "kernelstockcwm.zip") and select YES wait for it to complete
Step 5. using step 3 and 4 now select "SGH-T989-UnRoot_ROM_Zedomax" and YES.
DONE! Phone will be mostly stock, at least enough to return the device with out worry. (Zedomax's restored rom is dodexed tho)
Step 1. Download files to computer
STOCK TAR (Thanks to Przekret) Rezipped and checked files (Odined my self back to stock) and removed password
Step 2. Install the KIES program on your PC REBOOT then extract ODIN and the Stock zip file to a folder on your computer.
Step 3. Run ODIN and put your phone in Download mode. (Have usb plugged in the computer and Hold VOL +/- on the phone and plug USB in) Once you see the download mode screen hit VOL +
Step 4. Select PDA from within odin and navigate to the extracted .tar.md5 file and hit START. When it completes give 6-10 min the phone will automatically reboot for you.
STEP 5. Thanks to Mikeyinid If you get a boot loop reboot the phone into recovery (Volume up+down and power until Samsung logo appears after let them go. Highlight Wipe data/Factory reset and select with power)
Hope this helps, didnt really see a definitive howto with steps and working links.
OTHER LINKS THAT MAY BE DOWN
STOCK Kernel ODIN
Stock RECOVERY ODIN
Bubby's INSCURE KERNEL to root
Thanks to Bubby, teshxx, zedomax, and all you devs!