Well only one person suggests that, PVC t&e is not UV stable!
Nothing will detect a disconnected earth, only proper testing.
True, T&E in the long term will degrade due to UV. However this is over many years. On the mobile classroom installations mentioned we rarely had any problems (out of several hundred units) and mostly it was due to the taping used to hold the cable to the wire, neither did we have trouble with catenary movement causing the cable to fail (could be a problem on really long spans but most were around 5-8m. All installations were checked every three years so any degradation of the cable would be picked up in plenty of time.