A "normal" circuit breaker would likely never trip until you are cooked meat. Same with a GFCI breaker unless some of the current leaked somewhere other than through your body.
Basically, a normal breaker trips slightly above its handle rating, as does the normal breaker part of a GFCI breaker. So, a typical 15 amp breaker would allow many times the amount of lethal current to flow before it ever trips, which it would have no reason to do unless there was a sustained overload or a short.
Since the GFCI portion trips with current imbalance only, as long as there is no imbalance with the current that happens to be flowing in one arm and out the other, it won't trip either.