Indeed, I think disease will have a far far bigger role to play in any sort of population reduction as the result of declining oil supplies than starvation from declining food production. Especially as third world countries become increasing urbanised, living densely in horribly unhygenic slums, it will take nothing short of a miracle to keep disease rates from skyrocketing in the coming decades. It may well be enough to keep the maximum global population as low as 8 billion (as opposed to the currently projected 9-10 billion from various organisations). While this might be better for the planet, it will be nothing short of devastating for those living in such conditions.

simply put, we wont, the couple you name (typhoid, cholera) will be the worst. dehydration is the biggest killer. Remember to bring water to a boil and then let it cool to destroy pathogens.

Shortly after is the key word. TB was not entirely eliminated in all countries, however its prevalence was reduced to such an extent that the current couple generations have nil risk of contracting it. The same with smallpox. As to current trends, moving from 0 to 1 or 2 cases a year is bad(of the super duper bad TB), but compared to previous ages when sanatoriums were used to ease the suffering of thousands upon thousands I will keep the modern world thankyou.

And the Xtreme TB and super extreme drug resistent TB are caused by antibiotic administration which is not 100% effective (the same resistance eventually occurs with all bacteria)

http://en.wikipedia.org/wiki/Tuberculosis#history seems to back me up nearly 100%

It was not until 1946 with the development of the antibiotic streptomycin that effective treatment and cure became possible. Prior to the introduction of this drug, the only treatment besides sanatoria were surgical interventions,

this obviously only applies to countries where streptomycin is available in large amounts and cheaply to boot. wiki says 2 billion people currently have TB, with pretty much none in 1st world nations.