Re: is he still a US citizen ?
actually, it's my understanding that "foreign income" is NOT taxable unless you bring the money into the USA. So if you are an entertainer and earn money in, let's say, Spain, and you keep it in Spain, then I'm pretty sure that doesn't count as "income" until you bring it back into the USA. Similar for state income taxes (which vary from state to state, some having NO such tax), which don't tax income earned in other states. Notwithstanding, I Am Not a CPA.
But you STILL have to declare it and file your taxes every year. "Willfully not filing" - yeah, that's not a good thing for him. I believe Al Capone was taken down on tax evasion...