SELECT
	CASE WHEN CHARINDEX(':', A.DEPT)>0 
	THEN
	LEFT(A.DEPT, CHARINDEX(':', A.DEPT)-1) 
	ELSE 
	A.DEPT
	END
FROM
	(SELECT
	REPLACE( REPLACE( REPLACE (DB.Table.DEPT,'[NA1] ','') ,'[NA2] ', '')	,'[NA3] ', '') as DEPT
	FROM
	DB.Table) A

CREATE TABLE dbo.tblNames 
(
	ID int,
	FName varchar(25),
	LName varchar(25)
) 
GO

INSERT INTO tblNames 
 	VALUES (1, 'John', 'Doe')
INSERT INTO tblNames 
 	VALUES (2, 'Jack', 'B')
INSERT INTO tblNames 
 	VALUES (3, 'S', 'Fry')
INSERT INTO tblNames 
 	VALUES (4, 'H', 'M')
GO

SELECT * FROM tblNames