It's easy to underestimate Haymitch. He is a drunkard, but we must remember that he is a previous winner of the Hunger Games, and as such he knows how to win. In the first book of the series, Haymitch is crafty in sending Katniss gifts in parachutes just when she needs them most, guiding her to survival. Without Haymitch neither Peeta nor Katniss would have survived. However, in the second part of the trilogy, I think Haymitch's scheming is even more pronounced. He is deceiving both Peta and Katniss into thinking that one must help the other survive. Haymitch most likely believes that Katniss will be the ultimate survivor, if there is to be only one, but his true goal is to bring down the system that causes the Hunger Games to exist. If he must use Katniss and Peeta as pawns to achieve this goal, then so be it.