For the A's that was an 88 win team that lost a player that was worth seven wins over replacement. They would have never made the playoffs in 2014 without Lester. He and Samardza were the only two pitchers in August and September that could consistently get hitters out. So you remove Lester from the team and you got a team that might be competitive, but has no real shot.
They were not going to win a WS with that team in 2015, let alone the best division in baseball. The following year they would have then lost Samardjza, Kazmeer, and who knows how many other key components. At that point they would have been surpassed by improving teams like Seattle and Houston. With no minor league system to restock the major league roster, they would be screwed.
As it now stands they will have a year off, but they will be right back in the pennant race sooner than most think.