Technology. On most fundamental level, BPM consists of knowledge and technology. Technology is a way to accumulate, store and implement (execute) the knowledge. Technologies are superseding one another and quickly getting obsolete in ever accelerating cycles of technical revolutions, while the knowledge is a fundamental asset, which only grows in value with time.
Basic laws of mathematics and physics are known for several centuries and discovery of these laws shaped modern civilization. Computers appeared as manifestation of these laws and increased our ability of interpretation but did not change the laws as such.
Similarly, BPM is a way for discovery and interpretation of behavioral laws of large human collectives in their interaction with consumers and production facilities. These laws are also fundamental and change very slowly (if change at all). Professional BPM allows establishing islands of long-term stability in quickly changing corporate environments by accumulating and storing principal metadata and knowledge of the business.
BPM technology is just a tool to handle this knowledge. It does not matter, if a model exists in a form of BPMN, EPC, UML or whatever future notation to come. It does not matter, if a model can be executed or not in a specific BPM engine. However, it is crucially important that the model correctly represents all aspects of really running business.
If the model is fundamentally correct, it will easily survive and move across generations of notations, implementations and technologies, while serving as a driver for these innovations. Exactly for this reason there always exists a demand for business transformation services where syntactically consistent models and metadata serve as a ground and guarantee for smooth evolution of business.