Find termination and rehire dates
I believe I was right there at the beginning. Here is what I ended up using. Please advise if anyone sees any improvements. Thanks!

WITH CTE_GAPS AS
(SELECT P.Employee, pp.FirstName, pp.LastName,
    LAG(P.PostDate) Over(Partition by P.Employee Order By 
P.Employee,P.PostDate) GapStart ,
    PostDate GapEnd,
    (DATEDIFF(DAY,LAG(P.PostDate) Over(Partition by P.Employee Order By 
P.Employee,P.PostDate),P.PostDate)-1) GapDays
FROM dbo.PRTH P INNER JOIN dbo.PREH pp ON P.PRCo = pp.PRCo AND P.Employee = 
pp.Employee)

SELECT  P.Employee,
P.FirstName,
P.LastName,
P.GapStart,
P.GapEnd
FROM Master.dbo.Calendar C CROSS JOIN CTE_GAPS P
WHERE
GapDays&gt;29 AND
C.Calendar_Date
    BETWEEN DATEADD(DAY,1,P.GapStart ) AND DATEADD(DAY,-1,P.GapEnd)
    GROUP BY P.Employee, P.GapStart, P.GapEnd, P.FirstName, P.LastName