This will guide you on how to revive a bricked EMMC Galaxy S3 (for now only GT-i9300).
Now Windows compatible!
First step: Explanation
Caution: You will lose your EFS partition, but there’s not much to do about it.
This project is experimental in its nature and I take absolutely no responsiblity for anything that might happen to your device.
This is the work of Oranav and his i9300_emmc_toolbox repo.