I am a bit of a contrarian here (caveat: I don't have any specific industry expertise).
1) Insurance companies will only cover a small part of the (huge) addressable market and only for limited durations
2) Therefore, this class of drugs will become a consumer product, where the patient, not the physician drives the purchase made with their own money
3) This will drive prices down as supply constraints are alleviated and new competitors come online, the consumer market will still be very profitable at let's say $300/month vs. $1000/month and someone will step in and take that market.
4) The grey market will exist, not because big pharma is benevolent, but because it will never become more than a tiny fraction of the addressable market and will be prohibitively expensive to try and eradicate. In the US I am pretty sure that DHS will not be excited by having a bunch of its budget moved from border security to trying to find small vials of unregulated substance shipped by small Chinese vendors. Yeah, if its Fentanyl they care for obvious reasons, but I think the most we get in this market is a bit of "security theater" that scares potential buyers and makes it a bit harder and more expensive to acquire to keep the grey market smaller.