It's always safer to flash both the OS and EMMC images.. flashing only the OS leaves junk on the EMMC.. and settings.. settings that could cause problems (pointing to applicaitons now only half installed.. stuff like that)

However, even with a bricked device, I believe you should be able to turn off, connect to PC via USB and then access the emmc as USB storage, all without booting the OS..

This will let you back up your content (Everything in /home/user/MyDocs) even if it won't let you back up applications and settings (or conversations or contacts)

Not ideal..