Try this - short and sweet

;with mycte as (

select T1.Datecol, ISNULL(T2.Value,0) Val, ROW_NUMBER() OVER(order by T1.datecol) RN

from Dimdate T1 left join TotalsData T2 ON T1.DateCol=T2.DateCol

)

select Datecol,(select top 1 Val FROM mycte T where T.RN<mycte.RN and val<>0 order by RN DESC) val

from mycte

where val=0

UNION

SELECT Datecol,Val FROM mycte where val>0