In gliding the very last item on your pre-flight check list is "Eventualities" which covers the cable braking. As has been said you immediately lower the nose, regain flying airspeed, then land ahead if possible. If not you have the option of an abbreviated circuit or even a 180 if conditions allow.
The point is all the above is fresh in your mind because it's the last thing you think of before launching, so you carry out the maneuvers almost sub-consciously.
Still, gliders have vastly superior performance to SEPs and you can have a 3 or 4 minute flight from 1000ft before joining the circuit where as I would think twice about turning back from an EFATO at 1000ft in an SEP!