Personally, I think that a partial repayment would be reasonable even if Goat can afford the whole thing. The contract says "best effort", and the money probably was really lost and not just pocketed by Goat. Goat was apparently investing almost entirely in Pirate or other funds investing in Pirate at the time.

Maybe it would be reasonable to take the USD value of that BTC at the time of the contract and then apply the contract's compounding interest to this amount.