Oheyo, Urban brothers.
Emm, kinda, complicated situation goes right here. And that's a sad shit.
But, I've got something to write too.
All in all, in my opinion, deleting an old clan seems to me like digging out a root of an old tree. This doesn't really make a good sense to players, that were nurturing their clans. Pretty much intention and time was forced to make a really legendary clans. And now, you want to make clan system and TB better by deleting all these old non-active clans, that made pretty much for this game with interesting events, etc, etc, etc... And you think, that, to make clan system and TB better you should start with it? Huh? Really? If you want to dispose of these clans, you should offer something instead, like: board of and Old clans, where every dead or alive old clan could keep "living", just to retain oldish times of TB with its own thread and stuff.
Done.