The fabulous Donna Ballman (whose new book, Stand Up for Yourself Without Getting Fired, is coming out in September–you must read it!), wrote a great post on the same theme as a couple of my recent articles–what to do when your boss is trying to force you to resign.
Donna’s article is here: My employer says I have to resign, what do I do?
She gives a lot more information on when you should/shouldn’t quit. Highly recommended. (And not just because she quotes me.)