it's hard to brick the phone.
I tried repartition the storage, while flash an small flash file, so in theory, a "clean" partition of storage w/o any kernel and what not, and I could still flash the f/w.
that said, when it happens to me (when it's an empty partition), the phone will appear not to be boot up, and then you may find yourself not being able to go into download mode. chances are, the phone might appear to be power off, but its probably in a panic mode at the previous boot up, so there's no way you can change to download mode.
just take out the battery, leave it for 30s-1min, and then put battery back and then do the volumne down + home button + power button to bring the phone into the download mode.