Most bitcoin regulation scenarios would just be an ordinary investment risk, in some senses. If you invest in commercial property and then changes in the tax treatment of real estate mean that the value of your investment falls then that just sucks for you. I can't see that it's any different if, for example, the US Government started demanding annual declarations of crypto wallets on tax returns and started taxing capital swings as income.
If cryptocurrency is actually confiscated I'm sure that the US government at least will be obliged to pay out. Given the volatility of bitcoin (and the extent to which it will likely drop if governments come out full square against it) I'm sure there will be legal arguments about what the compensation for the taking should be. But if the use-case is largely either (1) speculation or (2) hiding things from governments and governments limit the upside of (1) with tax or structural changes and crack down on (2) I don't think anyone's going to make the bag-holders whole in case of regulation rather than confiscation. Bigger companies than ~$4bn have gone bankrupt by misreading their market risks before.