Unless Shireen's sacrifice magically stops the snowfall, which certainly is a possibility, I think Stannis gets trapped in the North, or maybe even decides to stay and battle the White Walkers after Jon reports back what he witnessed at Hardhome. Melisandre already said that is the true war and everything else is meaningless, which has never been more apparent.
Doubt it will happen this season, but it would be really cool if The Wall was overrun and an unholy alliance of Stannis, the Boltons, and Littlefinger(who's presumably leading the Vale's forced north) were force to band together to stop the WW from sweeping through the Northern Kingdom.