I'm so sorry, your child's father IS a junkie and you cant stop him dying or not.
Only he can influence it at all, and even then there's no guarantees.
I have only known one person who truly overcame smack. He was notably self aware and did everything, and I mean everything, in his power to get clean, stay clean and continue clean. He would be the first to say he'd been a junkie so knew he had control issues and knew his limits.
Sadly what he had previously done to his body left him dead before his DC's 18th anyway, but he did turn his life around before parenthood.
I had no choice not to be totally surrounded by smack for the first two and a half decades of my life. I've even breastfed an addicted baby as the only protective thing I could do for it, only to see the mother re addict it so she could have half it's methadone script too. It is the most pernicious of all the possible addictions.
The only good that came from the damage done to my younger self is I saw clearly how heroin destroyed everyone and everything, and decided to never take it no matter how much I wanted to escape what was happening.
It takes perfectly good and decent people and transforms them into liars and thieves and people who will endanger their own and others in every and any possible way, to get that fix. Boundaries melt away under it and the phrase 'they'd sell their own grandmother' becomes true.
It takes more average people and takes them to the same place faster, and it takes inherently bad people and swiftly helps give reasons to embrace evil.
Please stop dangling his child (via 'family') as something you can give him if he convinces you he's choosing her over heroin. Ultimately she's a saleable asset.
The people addicted to it who still have some un eroded morality left, always believe they'll be able to control dangerous situations they place their children in. They can't.
Heroin addicts with children often find themselves sought out and befriended by pedophiles. It's a hidden part of both worlds we don't like to acknowledge.
People think that pictures and films of abused children are taken by pedophiles. They often aren't and this isn't new. Desperate junkies will do anything.
Even those addicts who think they'd never go there, find their tune changes when faced with people who have the power to both jail them and end their pain or provide the means to.
Some parents end up abusing their own children to control and sanitize the process as supposed responsibility. The child finds itself complicit and trapped.
I am not saying that every heroin addicted parent does this, but generally it's because they've not been placed in situations where it's offered as simultaneous carrot and stick to get out of an immediate situation.
Their is just no part of a junkies world that is a good or safe place for children.
He doesn't want the implant because it doesn't only stop the high from smack. From the addicts POV: It sometimes has unpleasant side effects, and trying to avoiding unpleasant repercussions is part of an underlying junkies way of life.
From their POV: it endangers them by encouraging them to take larger doses to try to override it, which often leads to overdose, so they're smart to say no.
It stops most highs, and he still wants to be able to use something to get high. That's junkie wisdom and survival at play. He wants to survive, but he wants his options open.