If the page is archived, you have a few options:
- Publish the page and forward it using the Navigation options within the page
- Delete the page and set an alias AFTER you have deleted the page
- Rename the page and URL to allow you to put an alias on another page
- (last resort) If you must have the page archived, then leave the 404 page come up (not a good option IMHO)
There are others you could do I'm sure but these are the most common I work with. The catch with leaving the page in the content tree and having the same name/url is you can't create an alias on another page because it already exists in the content tree.