When companies break up, the employees, assets, and consumers are freed to be used again. If that doesn't happen, the company's operations continue to serve the existing demand and tie up resources, but there are no productivity gains, or possibly even diminishing ones. A zombie company is a company that should be destroyed by disruptive innovators.

This is the situation in recorded music right now. The major labels have consistently succeeded in winning strong copyright protection, so instead of collapsing, they are now seeing their position eroded by the innovators at a very, very slow rate; if it were not for the government's protection enabling the "copyright mafia" scenario, this situation wouldn't have happened and we would not have an unending trainwreck of music startups that try to reinvent the distribution process, but end up getting destroyed with fees or legal battles. The situation is so bad that it hinders even the companies that try to eschew all major label music(e.g. Jamendo), because the existing trade groups get in the way of non-traditional licensing schemes.