You don't need to flash anything, or an SSH access anywhere.
You just need to be able to boot into diags, and have access to the userstore. Drop the jailbreak (either one [tar.gz or stgz], at least on the diags version on my PW, although the number of reboots needed to trigger it might be different between one and the other, I didn't check) in the userstore, (re)boot once or twice into diags, and voilą.
If you broke your rootfs, but you still have access to the userstore, and no SSH in diags, you can try to just drop the official 5.3.0 update in the userstore and reboot, IIRC, it doesn't care (much) what state the partition is in, it will reflash it.
Last edited by NiLuJe; 11-18-2012 at 10:36 AM.