I has a quiz online for about a week and today I noticed it was "offline". I receive no mail message indicating why. What could be going on?

Check your quiz history log in the edit template, i.e. where it notes what date and time you created the template, submitted it, etc. It should say if it was taken offline by you, or by someone else. You may have caused it come offline if fixing something like a FITB answer. There are some actions that will cause a quiz to automatically come offline.

..such as changing either your intro or outro to something longer than allowable. I did that once lol.

Or editing the title a bit... I did that once.

Or changing the category.