This should get you pretty close... But I must admit, that I do not fully understand the logic... Why is there at 9401/Acc12 the "HasChild" set to 1 ?
Try it with this. The numbering is partitioned by the SourceCast. That means, that both sets (or many sets are treated as one set each, depending on the SourceCast. Additionally there is a running ID, like in your example:
CREATE TABLE Account(AccountID NVARCHAR(50) NOT NULL
,AccountName NVARCHAR(50) NOT NULL
,SourceCast INTEGER NOT NULL
,PRIMARY KEY (AccountID,SourceCast));
INSERT INTO Account(AccountID,AccountName,SourceCast) VALUES (N'11',N'Acc11',9401);
INSERT INTO Account(AccountID,AccountName,SourceCast) VALUES (N'12',N'Acc12',9401);
INSERT INTO Account(AccountID,AccountName,SourceCast) VALUES (N'13',N'Acc13',9401);
INSERT INTO Account(AccountID,AccountName,SourceCast) VALUES (N'11/11',N'Acc11/11',9401);
INSERT INTO Account(AccountID,AccountName,SourceCast) VALUES (N'11/12',N'Acc11/12',9401);
INSERT INTO Account(AccountID,AccountName,SourceCast) VALUES (N'11/111',N'Acc11/111',9401);
INSERT INTO Account(AccountID,AccountName,SourceCast) VALUES (N'11/11/001',N'Acc11/11/001',9401);
INSERT INTO Account(AccountID,AccountName,SourceCast) VALUES (N'11/11/002',N'Acc11/11/002',9401);
INSERT INTO Account(AccountID,AccountName,SourceCast) VALUES (N'15',N'Acc15',9402);
INSERT INTO Account(AccountID,AccountName,SourceCast) VALUES (N'12',N'Acc12',9402);
INSERT INTO Account(AccountID,AccountName,SourceCast) VALUES (N'13',N'Acc13',9402);
INSERT INTO Account(AccountID,AccountName,SourceCast) VALUES (N'15/15',N'Acc15/15',9402);
INSERT INTO Account(AccountID,AccountName,SourceCast) VALUES (N'15/12',N'Acc15/12',9402);
INSERT INTO Account(AccountID,AccountName,SourceCast) VALUES (N'15/111',N'Acc15/111',9402);
INSERT INTO Account(AccountID,AccountName,SourceCast) VALUES (N'15/15/001',N'Acc15/15/001',9402);
INSERT INTO Account(AccountID,AccountName,SourceCast) VALUES (N'15/15/002',N'Acc15/15/002',9402);
GO
WITH DistinctSourceCasts AS (SELECT DISTINCT SourceCast FROM Account)
SELECT *
INTO #tempHierarchy
FROM
(
SELECT SourceCast
,CAST(SourceCast AS NVARCHAR(50)) AS AccountID
,CAST(SourceCast AS NVARCHAR(50)) AS AccountName
,0 AS ID
,0 AS HierarchyLevel
,'' AS ParentPath
,'' AS ownID
,'' AS ancestorID
FROM DistinctSourceCasts
UNION ALL
SELECT SourceCast
,AccountID
,AccountName
,ROW_NUMBER() OVER(PARTITION BY SourceCast ORDER BY LEN(AccountID)-LEN(REPLACE(AccountID,'/','')),AccountID) AS ID
,Extended.HierarchyLevel
,STUFF(
(
SELECT '/' + A.B.value('.','varchar(10)')
FROM Extended.IDsXML.nodes('/x[position() <= sql:column("HierarchyLevel")]') AS A(B)
FOR XML PATH('')
),1,2,'') AS ParentPath
,Extended.IDsXML.value('/x[sql:column("HierarchyLevel")+1][1]','varchar(10)') AS ownID
,Extended.IDsXML.value('/x[sql:column("HierarchyLevel")][1]','varchar(10)') AS ancestorID
FROM Account
CROSS APPLY(SELECT LEN(AccountID)-LEN(REPLACE(AccountID,'/','')) + 1 AS HierarchyLevel
,CAST('<x></x><x>' + REPLACE(AccountID,'/','</x><x>') + '</x>' AS XML) AS IDsXML) AS Extended
) AS tbl;
UPDATE #tempHierarchy SET ParentPath = SourceCast,ancestorID=SourceCast WHERE HierarchyLevel=1;
UPDATE #tempHierarchy SET ownID=SourceCast WHERE HierarchyLevel=0;
WITH RecursiveCTE AS
(
SELECT th.*
,CAST(NULL AS BIGINT) AS ParentID
,CASE WHEN EXISTS(SELECT 1 FROM #tempHierarchy AS x WHERE x.ParentPath=th.AccountID) THEN 1 ELSE 0 END AS HasChild
FROM #tempHierarchy AS th WHERE th.HierarchyLevel=0
UNION ALL
SELECT r.SourceCast
,sa.AccountID
,sa.AccountName
,sa.ID
,sa.HierarchyLevel
,sa.ParentPath
,sa.ownID
,sa.ancestorID
,(SELECT x.ID FROM #tempHierarchy AS x WHERE x.AccountID=sa.ParentPath)
,CASE WHEN EXISTS(SELECT 1 FROM #tempHierarchy AS x WHERE x.ParentPath=sa.AccountID) THEN 1 ELSE 0 END AS HasChild
FROM RecursiveCTE AS r
INNER JOIN #tempHierarchy AS sa ON sa.HierarchyLevel=r.HierarchyLevel+1
AND r.AccountID=sa.ParentPath
AND r.SourceCast=sa.SourceCast
)
SELECT SourceCast
,r.AccountID
,r.AccountName
,ROW_NUMBER() OVER(ORDER BY SourceCast,HierarchyLevel,ParentID,ID) AS ID
,r.ID AS GroupedID
,r.ParentID
,r.HierarchyLevel
,r.HasChild
FROM RecursiveCTE AS r
DROP TABLE #tempHierarchy;
The result:
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| SourceCast | AccountID | AccountName | ID | GroupedID | ParentID | HierarchyLevel | HasChild |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9401 | 9401 | 9401 | 1 | 0 | NULL | 0 | 1 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9401 | 11 | Acc11 | 2 | 1 | 0 | 1 | 1 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9401 | 12 | Acc12 | 3 | 2 | 0 | 1 | 0 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9401 | 13 | Acc13 | 4 | 3 | 0 | 1 | 0 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9401 | 11/11 | Acc11/11 | 5 | 4 | 1 | 2 | 1 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9401 | 11/111 | Acc11/111 | 6 | 5 | 1 | 2 | 0 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9401 | 11/12 | Acc11/12 | 7 | 6 | 1 | 2 | 0 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9401 | 11/11/001 | Acc11/11/001 | 8 | 7 | 4 | 3 | 0 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9401 | 11/11/002 | Acc11/11/002 | 9 | 8 | 4 | 3 | 0 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9402 | 9402 | 9402 | 10 | 0 | NULL | 0 | 1 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9402 | 12 | Acc12 | 11 | 1 | 0 | 1 | 0 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9402 | 13 | Acc13 | 12 | 2 | 0 | 1 | 0 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9402 | 15 | Acc15 | 13 | 3 | 0 | 1 | 1 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9402 | 15/111 | Acc15/111 | 14 | 4 | 3 | 2 | 0 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9402 | 15/12 | Acc15/12 | 15 | 5 | 3 | 2 | 0 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9402 | 15/15 | Acc15/15 | 16 | 6 | 3 | 2 | 1 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9402 | 15/15/001 | Acc15/15/001 | 17 | 7 | 6 | 3 | 0 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
| 9402 | 15/15/002 | Acc15/15/002 | 18 | 8 | 6 | 3 | 0 |
+------------+-----------+--------------+----+-----------+----------+----------------+----------+
