The cables are like long springs. They are coiled metal cables that mesh with the teeth of the crank gear. Each tooth engages one spiral of the coiled cable to move the roof.
Unless the guy saw a flaw or crack in the cable, I'm not sure how he can say that it'll break soon - as long as the roof moves freely and smoothly. If the roof does not slide freely, I could see it snapping a cable.
I would give it a try, and as long as it slides back real nice, I wouldn't worry about it. If it's hard to open or close, I would remove the headliner and service the sunroof unit. Clean and lube.