2) The problem with this solution is that that's just another unilateral imposition of a broken redemption scheme on Goat, just a slightly less broken one. It still causes substantially the same problems. Two people can still come to Goat with possession of the same private key. Goat still has to decide whether to redeem twice or once. If twice, he's still getting massive liability crammed down his throat that he never agreed to accept. If once, then he's still taking the risk of being branded a scammer if Nefario issues the same code to two people, and he'll never even know whether it was Nefario or the claimant is lying. (Consider the same scenario as in 1 above.)
So two of your proposed solutions can't work.
No, you're wrong: All THREE don't work. What's stopping Nefario from relisting and giving himself ALL of each asset? How could you POSSIBLY prove that to be wrong? By this reasoning, MtGox is also a scam. Sorry, but at some point, you're just going to have to trust Nefario.
No. This is seriously incorrect and I think your approach is fundamentally misguided because of this confusion. The third solution does not require Goat to assume any risk he has not already agreed to accept.
If the assets are relisted, there is no way anyone can go to Goat and accuse him of scamming and there is no way Nefario can make Goat look like a scammer. Sure, Nefario can screw over Goat's asset holders, but they agreed to accept GLBSE to protect their ownership interest and it would be absolutely clear to them that it was GLBSE that had defaulted.
You are correct that with option three the asset owners and Goat have to trust Nefario, but only to the extent they have already agreed to trust him by listing their asset with him and purchasing them on his exchange. No new trust is required.
The other two options both require Goat to assume the risk that someone will claim that he is refusing to redeem a valid claim code and he won't know whether it's because of Nefario or the asset owner. This is a risk he never agreed to assume, significantly different in type from other risks he has agreed to assume, and frankly one I don't think he should assume. This risk does not arise in option 3.
In the absence of any redemption agreement, it was Nefario's decision to delist Goat's assets that directly harmed the asset owners.
Goat has never agreed to accept any arrangement where Nefario can make it look to his asset holders like he is scamming. Unless Goat agrees to accept this risk, there is absolutely no sense in trying to get Nefario to agree to impose it on him. It was Nefario's decision that harmed the asset holders and that decision appears to have been made without adequate justification to obtain leverage in another dispute with no consideration for the harm done to GLBSE's customers. You've been asked to investigate that. If you're trying to minimize that harm by moderating, you need to obtain permission from Goat and Nefario first. You can't force yourself into a mediating position, nor is mediating by ultimatums likely to be productive. You're supposed to be investigating.