I think that clan beef shouldn't go to the extent of "killing/ending" another clan's existence. Secondly, I think the amount of leaks clans use during a rivalry contributes to the demoralization process. Of course, people already know that having leaks prevents you (as a clan) from effectively making a battle plan against other clans. Lastly, pures could do away with the concept of ragging. Those are just a few key areas that could make it possible for these clans to return to OSRS.
At some point, people need to realize that every dog has their day. You won't win every prep, rivalry, or fight. You shouldn't sour over one singular loss whether it is a rivalry, prep, or wildy fight. Take the loss with dignity and show respect towards other clans. Bring back the environment that was present when the clan world was thriving in 2007-2011.