People are always the assets of an organization. It's always important to have the right mix of people and processes. People following the processes make the organization resilient and the projects have a greater chance of being successful.

Projects often go for a toss when a key person is no longer available. This can happen at the customer's end or can happen at the consultant's end. Thus, the responsibility of minimizing this from occurring lies with both the client and the consultant.

The best way to avoid these kind of pitfalls is to have strong documentation. Business Requirement Document (BRD), Functional Requirement Document (FRD), Requirement Specification (RS), and Scope of Work (SOW) can help mitigate the risk from the client's end.

From the consultant's end, it's important to have technical documentation. Documents such as architecture, UI wire-framing, and design document are important. Practicing coding best practices and having proper comments can minimize this risk.

Whenever a change of person happens, the consultant has to spend time with the new person in charge and ensure both are on the same page. The documents will also help to show what had been agreed on earlier. The change impact of a person leaving needs to be conveyed by the consultant to the stake holders, and at the same time, the consultant must ensure that he/she gives enough confidence to manage this change.

The impact is larger if project champion leaves the organization. This aspect has to be especially taken care of by the consultant. This risk can be mitigated to a certain extent if the consultant establishes rapport with all stake holders and is part of the meetings with the end users.