The same thing that happens now, except medics could know you're overdosing on pure diacetylmorphine (or whatever is sold), rather than heroin mixed with fentanyl mixed with baby formula powder mixed with your dealers skin sells mixed with whatever other garbage street drugs get cut with. Not to mention the money saved from being wasted on the war on drugs and gained from the sale of drugs could go towards mental health and other medical services to actual address the root of the issue rather than wasting even more money by throwing addicts in prison