You are correct about the corrosive influence the Clintons have had on the DNC. No doubt. However, you are wrong about their demise. In the past century each party has been pronounced dead every other election cycle. It is simply the way things are.
Obama represented a new face for the DNC, yet the responsibility either seems not to interest him or he is simply not the person for the job. A young minority candidate who spoke in hopeful platitudes with energy and enthusiasm is not the man we see now. As their standard bearer he shoulders as much (or more) responsibility as the Clintons. It may not even matter as he seems incapable of reconnecting with the “magic” that he rode to the Presidency or transferring that to anyone else.
The left still has plenty of adherents and money. What they lack is leadership. Politics like nature abhors a vacuum and it is certain that younger faces will emerge within a cycle or two. Don’t write them off - if American history teaches us anything it is that “the pendulum will swing back.”
They have a leader, but a supernatural one! These people sold their souls a long time ago.