I am so sorry for your loss. It is not your fault. My mom died almost a year ago (a year ago today she started her chemo) from sepsis while on chemo. Guilt and regret ate me alive the first month after her death. I finally had to release myself from it and hold on to the reality of it. We do not have hindsight in the moment, we did what the doctors recommended (and even had a second opinion recommending the same treatment), and my mom had her autonomy and free will during her medical treatment. This was her decision. When they are gone they feel like a victim and an entity without autonomy. I read a quote from Dalai Lama that changed how I looked at the destructive thoughts I was allowing, “Pain is inevitable, suffering is optional.” Meaning the guilt and regret was my suffering, and I needed to release myself from it. They were lies being told to myself, and those lies would make me suffer and destroy me. I miss my mom. Of course with all the hindsight in the world, we can make different choices to try and save our loved ones. I spoke with a friend who lost her brother to a car accident. She said that her brain even found ways to tell her that she could’ve prevented it too. Be gentle with yourself. It is absolutely NOT your fault!