HTTP Error 410 Gone
The 410 error also indicates that the Web server has no forwarding address for the URL, so can provide no redirection to the new Web server. This condition should generally be considered permanent. If the Web server does not know, or has no way of knowing, whether or not the condition is permanent, the status code 404 - Not found should be used instead.
You could (possibly should) include a 301 permanent redirect to it's replacement or related page so you don't loose the PR
If you go for the 404 error
option, it is advisable to make a custom 404 error page
c/w the navigation of the rest of your site. Why? So the visitor (and bots) have the opportunity to visit other pages on your site.