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As for the refund in BTC/USD, I wonder if there's a precedent for someone paying for services in something like gold, the market changing, and then being paid back in not gold and that being unacceptable. That would be interesting if someone could find a helpful case of something like that.
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1930s monetary gold was confiscated and gold delivery contracts that were specifically designed as a hedge were invalidated. If anyone wins anything from HF you will only get dollars not BTC and that's even if they kept the BTC since legal fiat is the only option when it comes to damages.
...which has nothing to do with whether or not a refund could be ordered in BTC, or the current fiat equivalent to the quantity of originally paid BTC. Gold in the '30s was the subject of legislation which BTC is not, and what happened with it then is not useful for determining what would happen with BTC now.