I was running recently into issues where I was not able to access my FRDM-KL25Z board any more, and ended up with a number of bricked boards.
This was *not* around securing the boards with flash erase disabled: this was about using Reset/SWD as GPIO, plus about Low Power modes.
To make the story short: P&E has a recovery utility released (http://www.pemicro.com/downloads/download_file.cfm?download_id=393, requires registration) which allowed me to recover my boards.
See Bricking and Recovering FRDM-KL25Z Boards: Reset, SWD Clock and Low Power | MCU on Eclipse for the full story.
I hope this helps, in case you are not able to talk with the debugger to an SWD based Kinetis.