IBM Case Manager is actually a product that sits on top of the core components of FileNet P8 and ILOG JRules. It uses the core component of the P8 Content Engine and Process Engine to manage content and workflows, respectively. Therefore, even with IBM Case Manager, you will still have the FileNet P8 and ILOG JRules files in your solution, but they will be hidden from the IBM Case Manager to some extent.
Besides some improvements in the installation and deployment process over the base P8, the biggest thing that the latest versions of IBM Case Manager bring to the table is the ability for the knowledge worker to determine which parts of the workflow need to be done on an individual basis. Traditionally, workflow designs in the P8 Processor Process were static and could not be changed at runtime. They still cannot, but Case Manager places an abstraction layer above the Process Engine to allow individual fragments of the process to still be statically defined in the Process Engine, but the overall process for the case was dynamic and determined at the time that the knowledge worker executed.
Moreover, if the project is intended for a process that is not related to knowledge workers, but only for system integration (for example, credit card approval), then the basic P8 and static workflows with ILOG JRules may better match.