I'm so sorry to hear about your loss. Although I can't answer your question. I am sympathetic. My husband died of a heroine overdose 1.5 years ago. It's a tough road but hang in here and talk about it. Frief can be very difficult.
Personally, I can't answer that question. It sounds like a medical/legal inquiry.
I can tell you that it's a small amount of methadone given 3 hours before the morphine but you don't say how much morphine or rubinol. It almost sounds like an allergic reaction.
What do the doctors say? Regardless, it's a tragic loss and you have my sympathy and best wishes. I hope you have plenty of support.