http://techinfo.toyota.com/public/main/2ndprius.pdf
There's only a very brief mention of the Emergency Cut-off in the Emergency Response Guide (link above). See the bottom of Page 13:
"The HV battery pack relays will automatically open to stop electricity flow in a collision sufficient to activate the SRS airbags.
I read that as only in event of collision, but it's entirely possible that the cut-off occurs via a seperate trigger than that which deploys the airbags.