Does the US need Pakistan?
Pakistan seems to think so. The linked article is one of many, in case you're not a fan of LA Times.
According to Pakistan, the US cannot afford to lose it as an ally.
Now, those of you who know me know that I'm typically not a very gung-ho, America F*** Yeah, USA #1 kind of guy. I subscribe to the whole "international community" and "one of many" ideals. I'm also not going to get into accusations of Pakistan collaborating with terrorist organizations, though I'm sure we'll end up there pretty quickly. But seriously, why exactly does the US need Pakistan? There's a major logistical route through Pakistan, and Pakistan reminded us of this by shutting the road down the last time tensions got particularly high.
Other than that, I'm not really sure what Pakistan is contributing. We give them quite a lot of military aid (including a quarter-billion-dollar upgrade for its F-16s, since fighter jets are great for fighting terrorists?) and we do have an interest in the nation's continued stability, as they do have nukes and we'd really prefer they keep an eye on those.
If Pakistan went neutral or hostile, how different would the war look? Would it change more than the war effort?