For the few reasonable quality questions I've seen (e.g. this one) where the OP has answered the question in an edit rather than as an answer I've usually:
- Suggested via a comment that answers should be answers.
- If the OP doesn't reply to that within a reasonable time period make an edit to correct:
- Roll back inappropriate edit to question
- Post an new answer as a community wiki (to avoid being accused of unfairly gaining rep for it)
This I believe is an appropriate course of action because it adheres to the "don't make moderators do work you can do without needing a moderator" principle, whilst sticking to the clean separation of Q&A design of the site.
If the quality is too low (e.g. it can't help any future visitors) then it's a vote close/flag. If it's unsalvageable I don't think there's much point editing something that will shortly be deleted.