According to this thread, one of the three criteria in filing suit to compel arbitration in federal court is diversity of citizenship.
Suppose Party A enters into a business contract with Party B. Party B sells the business to Party C in such a way that Party C inherits any previous contractual agreements signed by Party B.
Party A and Party C now dispute the interpretation of the contract signed between Party A and Party B. Party A and Party C live in one state. Party B lives in another state.
While Party B is no longer directly liable for the contract, he is able to provide testimony (if subpoenaed) regarding the interpretation of the contract that would be helpful to Party A.
Does any of this constitute diversity of citizenship in regards to federal jurisdiction? Or once Party B sells the business the fact that he signed the agreement with Party A and/or can testify as to the intent of the lease is meaningless?