Money will always exist in some form or another; will it be the USD?

Likely not; I think lots of banks and countries fear blockchain as a concept, because it dose allow the people to free themselves of the system, I don't expect it to happen for decades, but...

Imagine I worked only for bitcoin; what can the government tax me on? Imagine all transactions happen with some local currency that never enters, exists, or is controlled by a fed bank? What can they seize, control, or mandate? Same as I can make cashless trades and never pay a cent in taxes.

Thing about the above examples, people are slowly starting to do that, little by little - and if the government starts needing to defensively react to this phenomenon, they have in turn legitimized it as a currency that has value; and they're not the masters in charge of it's value, or how much of it is available.