The problem is that most likely, the eMMC is so hosed at a low level that the data is inaccesible.
There are some special tricks available (search around) for booting the I9300 off of a special SD card to repopulate the bootloader. So if you can replace the eMMC chip, you should be able to repopulate the bootloaders.
Another possibility is that if you can boot from an external SD, you MIGHT be able to send commands to resize the boot partitions downwards and back up. This will, in theory, cause a full chip reset. All data will be lost, but the damaged areas will get cleaned up. However, this is only theory based on reading the leaked datasheet - no one has EVER done this, so no one knows if it will work.
Ideally for these repairs we'd have an expert in JTAG recovery help out - I'm sure with the knowledge from that datasheet and a few dead devices, the RIFFbox guys could figure something out. I once emailed Josh at mobiletechvideos these new discoveries, but never heard back from him.