sounds interesting.
however this would only work decently for groups which have most of their files correctly listed in anidb.
and the other question would be if such a group status does really tell much about the availability of a release.
I don't think that a release by an inactive or dead group is necessarily hard to get.
I'd mainly see it as a quick hint whether one can expect more releases from that group or not - and whether it's useful to visit their channel or homepage. (Especially thanks to archive.org, the homepage-URL can be used even when that page is no more reachable. That's why I'd rather see that info preserved instead of a "no channel, no homepage, description:'group dead'")
I'd see it as a hint for st00pid users not to add the 7th version of a file to the DB because the 6 others don't have the same ed2k hash as the file they have on their harddisk.
I wonder why we didn't have the idea ages ago
I really think this is a good thing to be implemented because that might keep users from adding stuff to series that have been done and dropped years ago.
Also there should be an automatically added disclaimer to the dead group's info page where it says something like "Please note: this group is marked dead and therefor it is most likely the information on this page is invalid or faulty at least. Please do not expect to find any valid info on the pages or IRC channels listed here for they currently might have other owners than the ones formerly part of the Fansub group".