Heroin is an opioid. (although these days mostly is cut with fentanyl)
It is dangerous to go off cold-turkey - you definitely have to ween yourself off or it can be extreme hell and usually leads to relapse because the withdraw is terrible.
And yes there have been cases where people have died.
That's just so fucked, I feel bad for people who were simply in a low of their life and made one bad mistake who can never recover from it