Herr AlexUM,
When I started it was car- and winch-launches only. We were regularly subjected to cable-break training. In addition to that there were frequent actual cable-breaks seeing as we used wire because our landing strips were invariably gravel or sand, i.e. very abrasive to more 'high-tech' braided lines. The wire was not as strong, of course, and did not take kindly to rough launches. As a result the general standard of flying in this kind of emergency was quite acceptable. I gather that cable-break training, also recurrent cable-break training, is still very much the norm when engaged in winch-launching. (anybody still attach themselves to a car these days?)
Nowadays with launching being predominantly aerotow (and self-launching of course) I see no more cable-break training, which is my answer. The question you posed makes me think whether we should be training aerotow cable-breaks? Or is the risk unacceptably great when weighed up against the statistical chance of an actual break occurring on tow? Certainly I would not be very happy practicing a cable-break at 50 feet AGL with the end of the runway just disappearing behind the tug and glider, and I'm not sure whether a simulated cable-break within the safety-circuit - once at a more reasonable height than immediately after lift-off - would have much benefit, seeing as how that scenario becomes just another circuit, albeit possibly a somewhat shortened version. What do the brethren think?
On an aside, I have a scar on one lower leg from a bit of wire that penetrated to a depth of around two centimetres from a winch-launch that went awry. One of those early-fifties beasties where one sat right atop the contraption, blissfully exposed to the action, only nominally 'protected' by a little canvas awning. When the cable broke the loose end would flail around off the drum, pieces sometimes flying off in all directions. The cacophony of sounds was a little unsettling, as well as occasionally being pierced by hot little pieces of wire. Nasty things, winches.
Was für 'ne Mühle fliegst Du? Hals- und Beinbruch!