Timing belt snapped

Hi, My y reg rover is currently in my local garage. I had been experiencing problems with the water coolent leaking and when driving the car would loose power and shake for 3mins then it was fine again. The garage told me it was the manifold cover leaking. After they had it sitting in a sub zero compound for 5 days they phoned to tell me the engine had frozen solid and the timing belt had snapped because there was lack of anti-freeze in the coolent. Should they have checked this before they started it as they knew it had a water leak and water in cylinder one and it had been sitting in - conditions for 5days not used?