Bitcoin was worth that much when the contract was signed. It is the seller's responsibility to watch the value of his investments.
This.
Question: Since you bought all the real estate with virtual currency that's essentially monopoly money, no longer of any value, can the people you bought it from come back with hella judgments against for compensation in actual currency or otherwise repossess your holdings for non payment?
Not in the United States, that's for damn sure. Probably not anywhere. By the way, all genuine, non-rhetorical questions are philosophical by definition. Pondering a question is the fundamental philosophical act. Philosophy = Philos of Sophia = love of knowledge.
A good question is much more important than a good answer. Unfortunately, you have asked a shit question. Try again.