The solution would not be to delete simply them but to rename them for archive purposes:
Something like deleted_clanaaaxxxxx where the aaaxxxxx bit is some incremented character string.
Deleted players, clans etc would not appeari any league tables etc, but would appear in historical data such as games or group postings (with the new name). Clicking on the name of a deleted clan or player should bring up a window saying "this clan used to be aardvark assassins until it was deleted due to inactivity on date xxx" and additionally provide the same data that would have been given for aardvartk assassins just before their deletion.
The same technique would also work for players banned due to cheating.
Hopefully this is doable. It could be easier or harder depending on whether the user/clan name is the primary id for that element in the RHP database or not (I don't know).
Beware though - Personally, I stopped playing for a period of about 3 years and I have recently started playing again - so it would ideally be quite a long inactivity timeout!