Issue in replacing Cursor

I have a Cursor to be replaced build based on if exists condition , Cursor needs to be replaced because of performance issues.I am missing logic behind the If exists condition, So if any alternative to this Cursor with a similar Code is appreciated.

--Original Cursor to be replaced
DECLARE @sCaseID as int
DECLARE @sLastUpdate as datetime
DECLARE @sEntryDate as datetime
DECLARE @sUserID  as varchar(30)
DECLARE @sSystem as varchar(4)
DECLARE @sPrin as varchar(4)
DECLARE @sAgent as varchar(4)
DECLARE @sAccountNumber as varchar(16)
DECLARE @sExtStatus as datetime
DECLARE @sIntStatus as varchar(1)

DECLARE sample_cursor CURSOR FOR
Select 
S.CaseID, S.LastUpdateDate,S.EntryDate,S.UserId,S.System,S.Prin,S.Agent,
 S.AccountNumber,S.IntStatus,substring(S.ExtStatus,1,1) as ExtStatus
 FROM dbo.uvwView S
LEFT JOIN dbo.tbl1 A
ON S.AccountNumber = A.AccountNumber
LEFT JOIN dbo.tbl2  C
ON S.ECC = C.ECC
LEFT JOIN dbo.tbl3 T
ON S.Col1 = T.Col1 and
   S.Col2 = T.Col2 and
   S.Col3 = T.Col3
LEFT JOIN dbo.tbl3 D
ON S.Col4 = D.Col1 

OPEN sample_cursor 
FETCH NEXT FROM sample_cursor INTO 
 @sCaseID, @sLastUpdate,@sEntryDate,@sUserID,@sSystem,@sPrin,@sAgent,@sAccountNumber,
 @sExtStatus,@sIntStatus 
 
WHILE @@FETCH_STATUS = 0
BEGIN 

IF EXISTS(
 SELECT 1
 FROM TargetTbl TT
 WHERE TT.CaseID = @sCaseID
    OR (TT.CaseID IS NULL
        AND TT.AccountNumber = @sAccountNumber
        AND ISNULL(TT.CaseNumber,@sCaseNumber) = @sCaseNumber))

 BEGIN
        UPDATE TargetTbl 
       SET Col1 = '',
           Col2 = '',
           Col3 = ''
END 
ELSE 
BEGIN 
 INSERT INTO TargetTbl
Values('','','')

FETCH NEXT FROM sample_cursor INTO 
  @sCaseID, @sLastUpdate,@sEntryDate,@sUserID,@sSystem,@sPrin,@sAgent,@sAccountNumber,
@sExtStatus,@sIntStatus
END
CLOSE sample_cursor
DEALLOCATE sample_cursor

Thanks

Srikanth