Maintain consistent navigation throughout your site. If your navigation is always in the same place the user will learn how to navigate your site much quicker. This is the number one frustration from users. If the default page changes your link will still work. If your page contains this type of content it must be kept up to date at all times.
Bad information is worse than no information at all.
It would be better to provide an accurate link to another page or a phone number to call. When you add information to a page remember that it must be accurate and be maintained. Do your users really want to wait for it every time they visit your page. Don't include them unless they are really needed. Most users know that the web is always under construction.