Need to unlock a case which held by user and same time we need to update the case if the request comes from external systems. We not using optimistic locking we need only one user at a time to work. We should follow Sync approach so we not using JS or Queue processor here. Trying to unlock and update through the service API.
Queue based approach to retry and update when the lock is available is the recommended option. When user has a hard lock its better not to update the case from service activity this will have a serious data loss.