You can't reason with substance abusers when they're still using, because for all practical purposes they are not capable of it. If you report him and management are somewhere in the 21st century then he will be told to take a holiday and go into a recognised Rehab. program. When he comes out (4-8 weeks) he drives a desk for a couple of months & does 90 AA meetings in 90 days. Then he can start flying again with someone relatively senior in the other seat. He should expect random breath/blood/urine checks for quite a while. This is not a joke. One slip and he's out. Maybe he'll make it into stable recovery. Maybe he won't. That's up to him and his God.
Tough, but them's my rules in my outfit - worked so far.
If nobody does something firm before things become irretrievable then he'll end up disgraced and dismissed and quite possibly dead by his own hand (or screws up and take others with him).