If pirate pays out and Goat uses the money to buy back bonds, that is a breach of contract. The pass-through as described passes through as dividends.
All he would have to do is use some other money to buy back bonds slightly before passing through the payments as dividends. It's a pretty scummy thing to do, but it's not an explicit breach of the contract. It might be considered implicit breach, similar to constructive fraud.
Again, if an issuer of a bond buys back bonds at a discount with "some other source of money" they are defaulting in breach of contract. This is because bondholders who don't happen to have asks up will get the shaft if the bond later becomes completely worthless.
If pirate refunds all deposits and closes accounts, Goat should buy back at face value (
BTC1.00) using a bid wall.
If pirate provides a partial refund, Goat should pay that out as an equally diluted dividend, and let everyone know under what conditions the payout was made, and whether he expects further payouts.
The reason Goat can't buy back bonds is that the future payouts from Pirate are not certain and buying back would be deleting information. This is unfair if Pirate eventually pays sometime down the line.
Basically, Goat does not have the freedom to speculate as to what should be the fair price at which to buy back the bonds. He can only retire them at face value or pay out dividends of whatever Pirate sends him.