Bug#786657: apache2.4 in jessie/stable missing mod_imagemap
Forgive my ignorance, I'm not very familiar with the packaging structure for debian (beyond being a consumer) -- is Upstream from Apache? (I just went and downloaded 2.4.12 from Apache's site and I see in configure that you have to pass a parameter to actually enable compiling for imagemap. I assume this is what we're referring to?)
The site using these server-side maps probably has hundreds of them in use. Converting them to user maps is going to be a significant chore. While I can probably provide the guidance and suggestion to do so, I can't say that will be done in any short order, so for the interim yes the module is required.