Users delete their own questions
I've seen this a few times already. Someone will ask a question, and others will come comment, answer, and provide solutions. But once the original user is satisfied or dissatisfied with the responses, they will delete the question. This does no service to the next user whom will ask the same question or is searching UA for a solution. Sometimes the user will re-ask the same question after deleting their original question.
I realize users can delete their question at any time, but maybe that feature should be reserved for moderators. Maybe new users can flag their question for deletion instead.
I suppose it can't be helped. It's just something I thought about.
Sometimes the user will re-ask the same question after deleting their original question
You've noticed something's up; do some sleuthing :)
Sometimes though, yes, users delete a question after its answered. Usually, I find its because they feel they asked a stupid question and didnt want to leave the evidence.
Deleting is moderator and OP only. I've deleted plenty of my own questions :D In the past it has been possible to un-delete a question by accessing it through the user activity section. I've felt it necessary to do this a few times for the exact reasons you mention.