/**
 * Deletes a user account from the backend server.
 *
 * **Process**:
 * 1. Sends delete request with user concept ID and API key
 * 2. Backend deletes user and returns email concept ID
 * 3. Deletes the associated email concept locally
 *
 * Used for complete user account removal including associated data.
 *
 * @param id - The user concept ID to delete
 * @returns Email concept ID that was deleted, or undefined if error
 * @throws Error if deletion fails
 *
 * @example
 * const emailConceptId = await DeleteUserInBackend(userId);
 * console.log("Deleted user and email concept:", emailConceptId);
 */
export declare function DeleteUserInBackend(id: number): Promise<number | undefined>;