Five publications? Good God, you deserve a PhD more than me and anybody else I have known. FábioDias is absolutely right. I know of an identical case where the advisor wanted the student to do more work after six years and four publications...and refused to fund him AND wouldn't get him a TAship. He finally, talked to the graduate chair in our department. He was ready to go to the department chair and even the dean of the college...but it didn't come to that. The graduate chair immediately took charge, switched his advisor, emailed his thesis to three other faculty members to judge if his thesis was sufficient. He scheduled a defense. Half of the department (students and faculty) showed up. The abusive advisor was also present because he was kept as part of the committee, he was just not the chair nor the "advisor". He successfully defended and even the abusive advisor passed him.
He defended and left within a month.
You have done a lot of work and invested a lot of time and you definitely deserve your degree if you have so many peer-reviewed publications. I wouldn't recommend taking a leave because only rarely I have seen someone coming back after a break (whatever the reason may be for the leave) and finishing. And as you said, it will have financial complications and NSF wouldn't like it very much. In addition, would you quit your job a year later to come back to school? Or work part time? Start fresh with a new advisor, or continue the same project? Will you spend another four years with the new advisor? I would say that finish this as quickly as possible in your own favor. And how specifically would an email to the department chair reach the advisor first? Does he or his/department's secretary play golf with your advisor?
I would say, without writing anything, just drop by the office of the grad chair. Talk to him first. Tell him everything verbally. You should think very hard before putting anything in writing as in an email. Ask him for help. See what he does. If he takes control, then good. Otherwise just drop by the department chair's office and talk to him. This also avoids the danger of your advisor seeing your email first because there never was an email.
At the very end, I would compose a very careful email and send it to the dean of the college and/or the dean of the graduate school, making sure to CC both the department chair and the grad chair.
These are all different levels of escalation. You should start at the bottom, give them a fair chance and a reasonable amount of time to resolve this in good faith. But if it doesn't work, then don't be afraid to escalate it to the next level and repeat.
If you want to take it even further, there is the division of student affair and conflict resolution which is usually under the chancellor or the vice-chancellor. There is also the ombudsman office. At the very end, I would talk to the legal counsel at your school. In the US, even the hint of a possible litigation can have miraculous effects. The school's counsel will of course look out for the school but they might convince the school/college/department to behave rationally because the bad publicity is not worth a grad student.
I'd say hang in there. Research these offices in your university. Read up on some of these policies. Be reasonable and fair but also firm and assertive. I know you have put up with so much abuse but you have to start at the bottom and move up fighting for what's rightfully yours.