One of the reasons it is so important to periodically “ping” your contacts while working on a long-term project is that these “pings” will occasionally reveal that one of your important contacts has moved on, and is no longer with the organization (thus no longer very helpful…).

On the plus side, you often get in return an auto-reply with a new contact, and this is a good opportunity for a new introduction and restatement of your project’s message. 🙂