I highly doubt that any dealer would ever have access to carfentanyl or etorphine. These opioids are so potent that even if a drop of each were to be lace with heroin you'd have people dying left and right. They are used to knock out elephants, hippos, and rhinos. I think giraffes too. Not horses, however. I've heard of other fentanyl analogues being used to cut heroin but definitely not those two.
Correct those opioids are so strong that when researchers are making them, they not only have to wear full (and I mean full feet to head and back down again) suits that the chemicals can't get through... they are also required to all carry syringes and a SHIT LOAD of narcan incase someone accidently gets the tiniest drop of carfentanyl or etorphine (and we're talking a drop literally invisible to the human eye), because it will go right through their skin and they'll die immediately... unless their co-working hits them with an outrageously necessary dose of narcan... that's how potent and scary those are.
As far as your husband.. Sure he could have said he was trying to kill himself but you have to understand and come to terms with the facts:
1. He took 320mg IV dilaudid (i'm assuming it's IV) and a bunch of ambien.
2. He said he was trying to kill himself and that's why so many pills were missing.
3. You suspect the line about killing himself was just an excuse as to why he doesn't have any pills left.
4. The fact that he took that much and did not die means he has an insanely insane tolerance, and that means he must use a LOT.
5. Were he really trying to kill himself, and not trying to chase a high, and he was opiate naive or at least didn't take doses that high regularly, then yeah that many would have killed him,no doubt in my mind at all. But because it didn't kill him it tells me he's used to doses like that. People taking their meds responsibly who took that much, WOULD die, they wouldn't wake up and say "ahhhh man I was trying to die". They would die.
Sorry, he's lying. Drugs do that to people. But I'll tell you right now, if you love him, and want him back the way he used to be, then aggressive, angry and disappointed behavior will make him feel worse, and guess what he'll head straight for. Tough love doesn't work for junkies because it adds to their stress and desire get high to get numb. Be supportive, tell him you love him, tell him if he loves you he needs to stop, tell him you understand he cant stop all at once but tell him the needles have to go. Quitting opiates when you don't use needles is unrealistically easier (well compared to quitting when you're on the needle) to do. Ween him down a few pills at a time,, with his tolerance I'd say 5 pills a day minimum... remember you want him to have enough medication to keep him from going mad and getting violently ill, but at the sametime you want him to be physically uncomfortable with minor but liveable withdrawal.. that'll make the process quicker, and trust me, by day 3 his cravings won't nearly as bad, plus he'l be off the stuff much faster. When tapering it'sgood to take just enough to keep off seriously withdrawal, but allow minor withdrawal set in so your brain chemistry resets back to normal much faster., tell him you're proud of him when he makes progress and eventually,hopefully, he'll be able to quit (the taper will rid him of his w/d's when it's done) and your affection will keep him going. He will be tempted down the road, I promise you this, but if you don't yell at him, leave him, or otherwise give up on him and make him feel like life just gets shittier and shittier, he will get better. I promise.
The Dark Side forum here on Bluelight is an excellent place for support as well (just make sure to read their guidelines before posting there).