I have an answer voted -5 to this question, and I'm not sure if I should delete it. On the one hand, it's completely wrong and ludicrous. Yet on the other, there's useful comments and links that explain why my answer is sheer nonsense, and therefore possibly helpful. Yet, it's got one of the lowest ratings ever :|
As long as we're not talking about something that a moderator would delete (e.g. doesn't answer the question, is spam) - and you wouldn't post those things in the first place anyway - then it's really your call. You're not required to delete a post just because of its vote total, no matter how low that vote total may get.
Personally, I would delete the answer if I had become convinced that it was wrong and couldn't be fixed by editing. I wouldn't worry about preserving comments, because comments are meant to be transient. If you think there is useful information in the comments, edit it into your answer.
As David says, there are only 4 things to keep in mind: your answer isn't offensive, isn't a spam, it's answering the question, it is of very good quality. (Well, flagging an answer states only 4).
And as QMech says, you can always revert your post to a CW if you want so that your reputation (score) may not be affected in the future.
There is no rule that says, you should delete your answer. It's your wish, unless you're raged by a bunch of guys always against you (happens around SO everyday). You're saying that the comments are useful. So, you've got your point. Don't delete it if you don't want to. After all, it's worth a rep. score equivalent to a single answer. You can get it in the future, of course.
On one hand, There are a lot of users who've got more downvotes than you, and some users were lucky that their answer was accepted. While on the other hand, there are users who've deleted their 10+ voted answers when they got shot by an investigation on their cat art. Some mods should've seen a lot of voted answers deleted by this...
P.S. I've deleted many of my answers, due to these downvotes. In fact, I got raged by a guy once and when he's gone, I got all my score back. But now, I can't search where my deleted answers are. The reason I deleted my answers, I didn't want a guy to search my profile and downvote my downvoted post. But now, I don't delete my answers.
Speaking in general about a down-voted post, i.e. not necessarily about OP's actual post: If on one hand, one is worried about further deterioration of one's reputation tally, and if on the other hand, one really want to keep the down-voted answer, then making it a Community-Wiki (CW) may be a solution.
Write a new answer. Give the correct reason for the phenomenon, based on your new understanding. Then add a paragraph describing the wrong reason, and why it's wrong, based on those comments from the earlier bad answer. Explaining why frequently believed misinformation is wrong, is indeed educational. After the new answer is in place, delete the older wrong answer.
In theory, I like @manishearth's rule of thumb. In practice, I put up an answer that was inadequate (not wrong, but not well cited/quantified - eg, bad but fixable), and got downvoted so quickly that I pulled it before it took all my rep. As I'm a new user, I'm now below most privs.
(Would have added this as a comment below @manishearth, but guess what ...)