I've done fast roping from Wessex, Lynx and Dauphin in my time and the safety of the guys on the rope is very much uppermost in your mind.
In the Lynx we would have 2 or 4 ropes out at once and one of the drills was a flyaway following a simulated engine failure - this got the troops on the ropes to 'lock off' so they didn't keep going down the rope until they fell off. Flying with 4 guys underneath focusses the mind regarding height and speed!
Fast roping is still one of the best ways of air assaulting a building - and great fun (for the pilots).
As others have mentioned earlier, winching is a variation on a theme and you would brief your actions in the event of an engine failure so the winch operator could make the decision to cut the cable (if the winchman/cas were close to the ground) or winch in at max rate to try and get them safe during the flyaway.
I thought doing HEC for a TV show was poor TEM, especially given the terrain and confined area they were deploying from. It's one thing to do it to save lives (as in the Alps) but for simple entertainment???
They may have used a twin but, as has been discussed on these pages before, there's far more that can go wrong with a helicopter than just an engine failure and in pretty much every case, the people underneath are toast.