Um, to me, it isn't so much a matter of whether 'topping' a war is possible, it is whether the story is best served by ending it after the war.
I don't believe it is. I think it unlikely that Sasuke's redemption (or, alternatively, Naruto's decision to give up on his redemption and taking Sasuke down in a satisfactory way) can be resolved in the war. Even if the War cannot be topped, there's likely to be more STORY to be told. ...
Naruto's goal from the start of the series is to become the "hokage greater than any other hokage." (and, of course, to win Sakura's heart) His goal from the start of Part 2 is to "bring Sasuke back to Sakura" (presumably in a redeemed state)
How will either of these goals be resolved by the conclusion of this war without bringing about more story? He's not likely to be made hokage immediately after the war (when Tsunade was out of it, he wasn't even mentioned as a candidate -- the line of succession went from the late Danzo to Kakashi). Sasuke isn't ready to be redeemed, and if there's a battle between him and Naruto in this war, resolving what to do with Madara will either overshadow it (by losing in an epic duel with, presumably, Naruto) or will lead to its own additional story arc (by Madara sacrificing Sasuke in order to escape, robbing Naruto of his chance to fulfill the 'promise of a lifetime' and creating a situation where 'doing something with the escaped Madara' becomes Naruto's new goal).
Nah... the War isn't the end of the story. It might move it on to another phase, however... (another timeskip for the 'next generation' he said\hinted at bringing the story into, perhaps? Something to do with the Daimyo? The zombi ninja being released, and suddenly multiple generations of S-class ninja are -- instead of lining up in a giant army and becoming easily targetable -- suddenly moving on to launch a thousand of their own plans, any of which could be as bad -- if not worse -- than Madara's? The 5 great ninja nations collapsing as infighting about which will lead causing them to fall apart again, forcing someone like Naruto to bring them back together? An invasion from barbarians (i.e., a ninja-oriented version of Japan's Mongolian Invasion in the just-united-from-the-Warring-States-period)? Something else entirely?)
There is a lot being revealed in recent chapters... but much of it is more expansion of the fictional universe (which should create MORE room for additional storylines), not resolution of the existing storylines.
So, no, I definitely do not believe the War will be the last arc of the story.
Your post is very heartening. And so true. From a creative standpoint, the story is
not best served by ending it after the war. None of the goals set for Naruto would be necessarily achieved by winning the war. And, in fact, we know that the fight with Sasuke is going to be one-on-one, so it's going to have to be outside the context of a war scenario.
Madara is the one with the greater issue of world domination, so he is the driving force behind this war. Sasuke is just the conductor at the front of his own personal crazy train. He's going to do whatever the hell he wants, whether there's a war going on around him or not. So, looking at it from a motive standpoint, there has to be more coming beyond the war.
However there is another aspect that eclipses Kishimoto's creative choices here (meaning whether he feels the story is ready to end or not), and that is the marketing of the top-grossing manga to a worldwide market. Kishimoto may not have a choice as to when he'd like to end it. If it's at the top of its market, his editors, publishers and distributors may push him to keep writing well past a point he'd like to have stopped. But all that has to do with his contracts and who holds the reins.
I just think that as long as it's making money, doing well, sitting at the top, Kishimoto's editors/publishers are going to push him for more. Because as long as the main characters are still going strong — there's still a her, rival and love interest — then any arc that might look it's the last could easily be just another Pain arc (mass destruction and death, followed by a redmption and reset button).
...Lastly, I want it to continue as long as possible so I can continue to write my fanfic withouth feeling guilty that I've outlasted the manga!