Does the business case have relevance beyond the early stages of the project?
Short answer is – Yes it does. A useful business case is one that you evolve as you complete key milestones during the life cycle. At the end of the project, when you are going live with a new CRM operation, double check the business case and assess the costs incurred (both direct and indirect), and validate if the benefits have been realized.
Refer to the list of benefits you had conceptualized in the business case as you flesh out the requirements and design the system; ask yourself how exactly the features you build are translating to benefits.
As you are getting ready to deploy the system, ensure the benefits are realized by the adoption of the CRM system and processes by the users.