If, contrary to the position written up here, an asker changes a question after an (upvoted) answer is given because the asker wished to refine the question in order to get a different answer, should earlier answer be deleted (lest it garner downvotes from a later visitor who is unaware that they were proper answers to the question initially asked) or left as is?
I would say that the answer should not be deleted. We don't want to do something that might discourage users from posting valuable answer content. If answers are subject to deletion (or downvotes) because of a modified question, that could make people hesitant to invest time in posting good answers. Instead, the question edit should be rolled back, regardless of who made it. When rolling back the edit it would be a good idea to leave a comment linking to that Meta policy so that everyone involved understands what is happening, and why.
If the asker really has a different question there is a simple solution: create a new post and ask it. Asking questions is free (except in rare situations) so there is not much to lose. The only issue would be that the asker may be stuck with a question that they don't care about. I don't think this is such a big deal, and it may even cause users to spend an extra minute making sure their question is clear before posting, which (I think) is something desirable.
As far as I understand, the goal of the site is not to produce questions; it is to answer questions. During the early stages of a site's development it may be important to encourage more questions just so that the site can remain active. But I think that Mi Yodeya has reached the point where we can afford to put this small "burden" on the asker. We seem to get enough activity that I doubt there would be much of an overall negative effect from a user whose question edit was rolled back.
Of course, to the extent that we can, we should try to make everyone happy, and to that end we should carefully explain the policies and their implementation. But since the policy is in fact that edits (that invalidate answers) should not be made to a question after an answer has been upvoted, we have to enforce that policy by undoing such edits.