How long can we continue the treatment for a patient with damaged lungs? On lifesaving drug...?

Am so sorry to hear about your mom's condition. Not to sound insensitive, but did your mom have an advance directive? like if something like this is to happen, would she want to be on life support? If not, then maybe you and your family can talk about it. Sometimes, it is needless to let the patient suffer and just let them go in dignity. My father ped away o f cancer not long ago, we all agreed to have him DNR. Again, so sorry about all this.