Well for one, there will be a large backlash from the opposition, as well as the public - all pointing to the govt to say: "We told you so, we said we're being prostituted, have given our lives on the order of that country, and their President can't even step off the plane to visit us whilst he's in the region, let alone say thanks"
That will ultimately place the govt in a pretty difficult and indefensible spot.
When someone you know, someone you consider your friend comes to your town after many years, you expect them to pay you a visit. But they don't, so that hurts. That hurts in Indian culture, that hurts in Pakistani culture too, hain na? But what if that person comes, visits your neighbour, whose house is to your right, and then visits your neighbour, whose house is to your left, but then doesn't knock on your door and leaves. It hurts even more doesn't it? Especially when you've done so much for them.
Taking that analogy, you can see this will cause resentment and consternation across the board. It will reinforce the suspicions and anger towards the US, not lessen them.
The govt is weak, it's seen as the slave of the US, and this will be a huge slap in the face, a massive snub. The consequences will be a media on the rampage, whipping up emotions, a public charged, the opposition (PML-N, PML, Islamic parties, PTI), all emboldened with a big stick to beat the govt. How can the govt save face? What can Zardari give as an excuse?
Unfortunately in many cases we've seen, we operate on a tit-for-tat basis when it comes to treatment accorded to India. Nuclear deal, military hardware etc. Anything that is a +1 for India, must be a +1 for us. That's the mindset, as petty as it might sound. So if he's visiting India, smiling and shaking hands with MMS in Delhi, he must do the same in Islamabad.
Skipping a stopover in Pakistan would be stupidity of the highest order from the US. The political equivalent of Obama handing the noose to Zardari & co.
My 2 cents.
