To add a
little note of seriousness...
This technology is being / has been developed for road cars and if there is ever a significant proportion of hybrids in the road car fleet I would guesstimate that there is far more likelihood that a hybrid road car would be involved in an accident than a hybrid race car.
So to paraphrase your question...
how safe will these things be in the event of an accident or breakdown?
All I can say is that (IM(not so)HO) if safeguards are not in place to guarantee their safety in the event of an accident or breakdown, hydrids will never be allowed to be sold to the general public!
However, I can name 2 hybrid cars already on sale to the general public... the Toyota Prius and the Honda Civic ... so somebody somewhere must be convinced they are safe.
In fact, there are systems in all modern vehicles which are designed to work only in event of an accident (airbag systems, for examples) so surely they can also design systems to isolate / discharge and high voltage systems as necessary after an accident.
I will now remove my "geek's" hat
and return you to our normal service.
PJ