--@my_Table_ids is a user defined table type that is a list of PK's

--This INSERT works just fine

INSERT INTO dbo.MyMainTable 
(MyMainField)
SELECT
MyMainField
FROM dbo.MyMainTable_TEMP WHERE MY_PK IN (SELECT id FROM @my_Table_ids)	

--Now, I need the new list of PK's that were created 
--above and update another table that which
--also contains the list @my_Table_ids

--NOT SURE ABOUT THIS UPDATE for the WHERE clause

UPDATE MyXTable SET 
MY_MyMainTable_FK = (SELECT MY_PK FROM dbo.MyMainTable WHERE) 
WHERE MyTempFK IN (SELECT id FROM @my_Table_ids)

DECLARE @MyTableVar TABLE
(
	id BIGINT
);

INSERT INTO dbo.MyMainTable 
(MyMainField)
OUTPUT INSERTED.MY_PK INTO @MyTableVar
SELECT
MyMainField
FROM dbo.MyMainTable_TEMP WHERE MY_PK IN (SELECT id FROM @my_Table_ids)	

--BELOW WON"T WORK???????????

UPDATE MyXTable SET 
MY_MyMainTable_FK = (SELECT MY_PK FROM dbo.MyMainTable IN (SELECT id FROM @MyTableVar))
WHERE MyTempFK IN (SELECT id FROM @my_Table_ids)