ford mondeo 08 diesel 2ltr injector leak off pipes?

2 weeks ago smell of diesel in my mondeo and the garage who repaired it said it was due to leak off pipes leaking and they duely replaced them. I have used the car sparingly since then and a couple of days ago i put the heater on as it was quite a cold day. I noticed after a while that it was only blowing cold air and the fan was still running after i switched off the ignition.back to the garage this morning to be told i probably had cracked the engine due to no coolant in the system. 2 questions really firstly no indication or warning on the dashboard of any overheating problems and secondly could this be something caused by the original repair.