How many coaches who have taught the Buffalo Sabres have died?
have died means deathYear is not NULL; Buffalo Sabres is the name of team;
SELECT COUNT(DISTINCT T3.coachID) FROM Coaches AS T1 INNER JOIN Teams AS T2 ON T1.year = T2.year AND T1.tmID = T2.tmID INNER JOIN Master AS T3 ON T1.coachID = T3.coachID WHERE T2.name = 'Buffalo Sabres' AND T3.deathYear IS NOT NULL