We often get the case of someone asking an off-topic question, getting one or more answers, and then the question is finally closed. In some cases the OP even accepts one of the answers.
This leads me to wonder if answers to an off-topic question should be deleted?
That depends. Are the answers useful? Is the question fixable? Is the close-worthiness borderline or blatant?
I can't speak for others, but if I saw a question that seemed appropriate and invested effort in writing a good answer, only to have the question closed and my answer immediately deleted, I'd be less likely to contribute answers in the future. Now if I'm jumping onto crap questions to try to score some rep before the inevitable closure, then you want to discourage that behavior. But be careful about what else you're discouraging if you make a blanket policy.
I do favor deleting answers to questions that clearly shouldn't have been answered in the first place. But I think we need to take them on a case-by-case basis. The community can help by downvoting, flagging, and reviewing, or by bringing up specific cases on meta where it's not clear what to do or some extra help is needed.
Also consider questions that were on-topic when answered and then there was a policy change. Sometimes they get deleted, sometimes they get historical locks, and sometimes they stick around. I don't think we can pick one of those and apply it to all cases.
Since closed question tends to stay around for a bit, other people see that a question is closed but they also see that the question got answers. I believe this may lead other people to post a question without worrying too much to know if it would be on-topic because they know they will have an answer anyway.
An even worse case scenario is when people refuse to make they question on-topic because they see that they have answers (this was the case here, currently the question has been edited again by someone other than OP to make it on-topic but I worry that OP will rollback the changes a 3rd? time).
I think that, if we delete answers from an off-topic question, people will stop answering questions that, they believe, might get closed and will, instead, try to prompt OP to make the question on-topic (which will lead to more quality questions \o/).
Another problem to answers to an off-topic question is that bad answers might to not be downvoted because: "why waste my downvote (who cost reputation) on something that won't be deleted?".
And because why regular users with downvote privilege would waste their time reading an off-topic question? The problem in this second case is that not-so-regular-user with upvote privilege might read the question and upvote the answer, even if the answer isn't backed-up and might contain terrible advice (if it's not backed-up, you might not realize that the answer is terrible).
Also, since the answer is closed, the terrible answer can't be challenged by another answer that would have been written after reading the terrible answer.
