MfgTool can recover any kindle that is not physically broken. You just need to be patient while we get all the pieces in place to do this. My kindle can boot into fastboot because I have done damaged fastboot stored on the mmc (yet).
With the right profiles, MfgTool can flash partitions from images just like fastboot, but by using the USB Downloader mode, instead of a flashboot module inside bist u-boot saved on the mmc.
fastboot is simpler and runs on more devices, but it needs firmware support. USB Downloader mode is built in and cannot (afaik) be damaged or removed, but is different for each different processor.