Certainly some material from Feast
will leak into the end of season four; short of massive padding there's no way the King's Landing material after the Red Wedding can be stretched across ten episodes. Ditto Arya, who has all of two post-RW chapters in A Storm of Swords
. I wouldn't be surprised either if season four carries Bran through his first two chapters in Dance
, all the way to finding the three-eyed crow; even with introducing the Reeds, his four chapters aren't going to fill twenty episodes. By contrast, his third and final Dance
chapter could cover at least half a season by itself.
I'm less confident that the series is guaranteed to go the distance; it's expensive, it's only going to get more so, and the ratings will peak at some point. Season four will actually represent a comparatively tempting endpoint, since the closures originally planned to set up the five year gap are as close as the show is going to get to resolution any time soon. There also has to be some awareness that catching up to the books would be a very tricky proposition all around. Once we see what the rest of this year's ratings are like, it'll be easier to be optimistic.