Cash works when there's no power, or internet
Cash works even when you're a repressed minority
Cash works when you can't afford a bank
Cash works to route around damage, no matter the source.
Some people will still want to deal in cash, so if the government doesn't provide it there will be some other kind of barter. Gift cards, those printed Bitcoin notes, foreign cash, gold or something else.
NO
That's the only reason Rothschild etc, New World Order headers, think they will keep on ruling the world with founded base in US
Those millions of people would stop cheating on taxes only if the IRS receives significantly more funding as well as a mandate to vastly improve its detection of suspicious financial activity and increase the number of audits.
The IRS would receive more funding and a new mandate only if (a) Republicans massively lose in Congress and then (b) Democrats decide to burn their advantage on a very unpopular measure.
Tl;dr the US will not go cash-less in the foreseeable future.