Smoking opium. Opium is a drug that gives the exact same type of high as any other opioids, you just need a lot of it compared to fentanyl, I feel like it would save the lives of fentanyl addicts and greatly reduce, or even eliminate the chances of an overdose, opium has been used by people throughout the history of mankind, in my opinion, I consider it a superior natural alternative to synthetic medications, such as suboxone and methadone when it comes to aiding in opioid withdrawals and cravings.
Disclaimer: I do not endorse nor encourage opioid use, this post was made with the intentions of having a last resort option in case the worse of the worst happens: A relapse.
Edit: one more thing I want to point out is that this is just my idea, and my opinion. I forgot to mention. Never use alone and ALWAYS carry narcan.