If they miss out on Playoff then no, this season was not a success because that was the main reason they stayed as is, was to win the Division.
Plus
This is not a young an up and coming roster, most of these guys won't even be on the roster next season or the following, so it not like these guys are in a learning mode or whatever you wanna call it for competing and playing in important games in September to gain that experience for next season, If they end up out of the playoffs it'll just be like a fake 9th inning rally and a disappointing loss.