I think static playlists and especially external playlist files have always been of little importance to many MC users. Smartlists and view scheme configurations are for most users possibly more or at least as important. This may be a surprise to someone who has previously used programs that are very playlist file related like old Winamp versions etc.
Instead of copying playlist files from a library to another many users transfer complete libraries with all the goodies (including view schemes, all playlists, database info for untaggable file formats (like video), import dates, CD/DVD database, etc).
We have had several threads about sharing and transferring libraries between the PCs on a LAN. A very usable solution is to share the actual library folder if it is enough to use only one MC instance at a time for updating the library.
That said, and as I already said, I agree that Auto-importer could automatically check the presence of the source playlist files and remove the deleted files from the Imported Playlists group too.