Not an official thread, no. Partly because- if they disappear with no goodbye thread- how would we know they had died rather than just left the forum? Seeing as it's anonymous.
Also, I think listing actual deaths in one convenient place would be the sort of ammunition journalists love I imagine. Obviously, they could still go hunting themselves but, it would make it so easy for them to have it all in one place.
I know what you mean though. A memorial type thread is a lovely idea. I just think it would more likely be used for other purposes though ultimately.