My guess is three months. Long enough for the publicity to die down, and for Camille to pay a couple of doctors a million dollars to swear under oath that Cosby is terminally ill.
Because the rich don't face any real consequences for their actions in this country.
Prisoners die in prison all the time. Unless he gets an appeal, he'll do his 3 years and be released if the guidelines say that well behaved prisoners get parole. The only thing that could deny parole would be the statement that he is a "dangerous sexual predator". This could push the parole board to say that he should not be released.
Given that he didn't use physical force to rape women, he used medicine, you could argue that the threat has not be lessoned by age and fragility.