I think any court would find the terms of the contract insane enough to make the whole thing null and void.
And also that Goat owes Gurrty the full principal, if Gurrty can establish that he sent the money.
In a nutshell: If it can be established that you gave me a million dollars according to some completely insane contract, and the contract is found to be invalid... I don't get to keep the million.
A court would also interpret the principal in terms of fiat value at the time.
It's not reasonable to expect Goat to pay millions of dollars because he stupidly lost a few thousand dollars years ago. At the same time, Gurrty was denied the chance to maybe make lots of money by holding onto the BTC, so he deserves more than just the principal IMO. But not the full BTC amount. (What are the chances that Gurrty would have held onto this BTC until now if he was so careless as to loan it to Goat?)