Many will fold already and sell what they have on the first letter they receive. The remaining will resist as long as they aren't threatened with jail especially if you have a family.
You will be held...
I’m certainly not an optimist, but I also think a prerequisite for this scenario is that Bitcoin is worth a shit ton. Then, all of the extremely rich bitcoiners will have had to fail at influencing the government with money, which is how our government works. Additionally, large scale crackdowns on unrealized capital gains would probably lead to bitcoin crashing severely, resulting in a whole lot less tax money for the government.