They definitely messed up the Briere/Drury thing. But, regarding Vanket, it doesn't matter if the Oilers were going to do it or not. I doubt they told the Sabres on 7/1/07, that they were going to do it. Both Briere and Drury were gone by the end of that day.
From what I understand, the Sabres didn't hammer out the Briere extension, because they really wanted Drury more. I have to say, I did, too............Another move that looks bad in hindsight.