I agree on not knowing what will happen north of the wall. But lets be honest, benjen is most likely not alive anymore, and even if he is, the life of one isn't as important as the entire realm. Also, it doesn't really matter what threat or battle will come because we all know, it's about the others, and they can't pass the wall. And the wights, highly doubt they can climb that huge wall with the small intelligence they have, and wights are a lot easier to beat than white walkers. I think it would've been smarter to seal it off since the only reason they didn't before was because of the wildlings, but those are no longer a factor anymore. Ofcourse it wouldn't make a great story line, but that's just my thoughts anyway. Thanks for replying.