Pentru a calcula diferenta dintre 2 date calendaristice poti utiliza functia DATEDIFF: ms-help://MS.SQLCC.v9/MS.SQLSVR.v9.en/udb9/html/57e0601a-9d97-4437-9be1-7efa639b39fc.htm (copy + paste in Books Online - sectiunea URL).

In cazul tau poti formula conditia din IF astfel:

IF ( DATEDIFF(dd,@DataFinalizareContract,@GETDATE()) <= 4 )