Welcome to WebmasterWorld Guest from 18.104.22.168
Since the html pages are no longer available,
If that means the old pages are actually no longer available, as in they have been deleted from the server, you don't need to do anything else.
It's not necessary to delete the unuse channels unless you're a neat freak
On a side note, you did remember to 301 redirect those pages to the wordpress pages right? Nothing worse then getting bombed by google due to not redirecting properly.