Fathers Death due to Sepsis and Septic Shock

My father died due to septic shock the leading cause of death written by the ICU doctor. septic shock or sepsis has to happen following infection and they couldn't diagnose where the condition was. But all this started after doing the peg tube insertion procedure by a gastro doctor on my father who is 77 yr old person with comorbidities. So, is there any use if we go for filing a case against the gastro doctor for medical negligence or malpractice? We are not aware of any of these. They had taken signature consent from us before doing the procedure. Also, they informed me there is a cancerous doubt seen in the lungs. But as we don't want to hurt our old age father with biopsy and chemo, we did not go for further investigations on that. This was the major piece of information. But the main reason for infection was caused after the procedure due to the doctor's negligence during the procedure, causing air leakage and pus formation which led to septic shock.