What would you do?

So My mother in law sort of went "missing" my sister in law was taken to hospital by her because she was borderline prem labour. She left her abandoned there and no one i know has been able to get in contact with her since Friday afternoon. Pretty sure shes out on a crack bender with her other daughter. My partner wants to file missing persons report but idk Looking for advice not judgement i already know its fucked up.