I think there are two kinds of writer's block. One is a general malaise "I don' wanna" which is (in my case) usually brought on by having screwed up the book somewhere and having consequently run into a wall. In order to get past it I have to suck it up and go back and fix the problem, and then go forward from there.
The other kind is brought on by systemic stress, and it leaves writers in a place where they cannot get beyond the (illlness, financial difficulties, family dynamics, lawsuits; name your stress of choice, it'll apply somewhere) stress to work. This is much, much worse than "I screwed up and gotta fix it to go on," obviously, and it can take years to get through, much less recover from. For me personally, the Negotiator Trilogy *itself* was such a source of stress while writing that I still don't want to go back to that world to write full-length books; it was years before I was even willing to consider writing stories in it. So at best these things take time to work through, and at worst, writers never recover.