@Developereo,
Someone with a better background in economy can better answer than me. Nonetheless, here is my understanding.
My understanding is that the US 'aid' goes into compensation for the military operation carried out by 100,000+ Pakistani troops in the Pakistani northwest. Pakistan is a very poor country and 100,000+ troops are lot to deploy in combat missions over extended periods. Sadly, Pakistan will have to cut back on some of the operations/deployments against them--and there have been many in FATA alone over past several years. The damned terrorists will be so happy that finally the heat is off them--and believe me, drones are nothing compared to the Pakistani military operations against them.
Pakistan will start saving money by cutting down the operations.
However, it is not the American 'aid' which is the pivotal consideration here. It is the trade with the West. The IMF loans. Even foreign remittance can be choked off by some legal ways. Even without the UN approval, the West, under American directive, can hurt Pakistani economy big way.
Default is almost certain.
What happens in a loan default? I don't know.
My educated guess is that, unlike closed, tyrannical countries like N. Korea, Pakistan has a lot of collective wisdom, pluralism, democracy, natural resources AND powerful foreign friends who can ensure a defaulted-Pakistan continues to feed its population. This will call for a revolution of sort: Different parts of the population coming together on some interim setup. I think it is entirely likely. Pakistan have done so in 1971, 1988, and 2008 (E. Pakistan war and its consequences; Zia's death; Benazir's death and elections; respectively) where the ruling classes buried their differences for some minimal common agenda.
Remember that: Pakistan has significant civil society, free judiciary, very philanthropic population, free media, and media class, great agriculture lands, working services and industries, along with a powerful military. Things are not as bad as the noise make it out to be.