Stump Grinding

I hired a company to grind 2 stumps and we broke a pipe. Since the sprinkler heads were about 6 ft away, never crossed my mind a pipe was wrapped by the roots and buried only around 4 inches down.

I have 2 questions: Would I be liable to fix the pipe (any way I already fixed it but want your opinion) and anybody did any kind of agreement or contract for this kind of job to protect yourself from unforeseen situations like that?

Thanks