to reduce the chance of being dragged at speed in surf and cold water, perhaps a tether that will disengage the mainsheet when activated?

Like Jake's snapshackle, except it would release the mainsheet block from the traveler or something like that...? That would at least depower the main which may slow or stop the boat.

This might make it easier to swim back to it and get back on rather than watching it sail merrily off into the sunset (or rocks)