I keep writing it. I've been doing that for about a year now. Sometimes it sits there for a couple months with no work, sometimes I write more every night for a week. It's been good for me in some ways, but I have to be careful to pick times to write when I'm not overly depressed, because dwelling on it doesn't help.
I think it's very much like therapy, in that forcing yourself to keep going isn't a good idea, unless it's done for the right reasons. The right reasons being that you know it'll help you when it's done, the wrong reasons being because you feel obligated to produce something for others to read. Unless of course, that helps you Also, like therapy, it's good to have a supportive environment to go to if writing it gets to be difficult for you.