Create a Redirect for a page if its unpublished / deleted
There is a module that does much of what you describe: Save Redirect on Delete.  It will push the user to a predefined page and you could put popular items on that destination page.  

If you want the recommended content to be customized for the page they tried to reach you'll almost certainly want to build something custom. This module would probably give you a starting point, but in addition to what it provides you'd also need to preserve some kind of taxonomy reference (or similar) information to be able to provide something sensible.