Forget all the DIR'ness discussions, equipment, gas planning, etc. This aspect of your post is what concerns me. There is absolutely a lot you could have done, and should have done, if your buddy went missing. True enough, if your regs are freeflowing and you've lost contact with your buddy surfacing is your only option. But once you reach the surface you're not relieved of your duty as a buddy. This is not DIR training, AOW training, or even OW training- this is just common sense. There's a missing diver. You are the only person that knows this diver is missing. How do you know that something akin to your double freeflow didn't befall them as well? I see it as completely unconscionable that you didn't do something after you surfaced to address the fact that your buddy was missing.