Board Thread:Support Requests - Community Management/@comment-5847836-20130312224418/@comment-10688548-20130313140546

If you take a look at Help:Merging wikis there is an established process for this.

The page declares that you should "Secure both admin & community support on both wikis for the merger." This shouldn't be a problem to do on your wiki, however the other wikis are clearly dead as you say. I've been told by Staff that even if the smaller wiki is mega-dead, you should make a good-faith effort to inform the admins, post a big notice on the main page, et cetera, of your intentions to merge. If there is any actual content, you should move it to your larger wiki (consider using Special:Export and Special:Import).

Unless there is any objection after a week or so, you should be able to Special:Contact/general and have the wikis closed and redirects made.