I had mine done recently at my local Indy - they have 2 ex VW trained mechanics - they have not had 1 failed VW mk5 cam belt. and some had done quite high mileage before being replaced.
BUT what does fail are the cam belt tensioners, asst pulleys and bearings and the water pump. Not all together and not in that order! Any of those let go and you are stuck.
Cam belts can break or the teeth can strip off - it is documented. If that happens, especially at speed, then an engine wreck is likely. You might get away with bent valves and a damaged head, but is it worth it?
I had all parts changed plus coolant, for peace of mind.
And I had the 'bypass thermostat' changed at the same time as it was drained down - nice quick warm up now. It was stuck fully open!