Yes, you can use nested case statements, but it gets real ugly real fast. Try this:
CASE WHEN @variable = 1
THEN (CASE WHEN CASE WHEN tbl_column_id IN(SELECT tbl_column_id FROM Table)
THEN 1
ELSE 0
END
AND CASE WHEN othr_tbl_column_id NOT IN(SELECT othr_tbl_column_id FROM OtherTable)
THEN 0
ELSE 1
END
ELSE 0 END