I dont think money will ever be obsolete although it may change forms. For example Constitutional money (in the US at least) is silver and gold but these days we have worthless paper and cheap metal that is supposed to represent actual money.
After wiping out 90% of the world's population: by conning us all into fighting a holy war between Christianity and Islam, deliberately starving millions to death and manufacturing pandemics to kill off even more, the architects of the new world order will have the survivors fitted with radio frequency identification chips embedded under the skin. These chips will be used to identify, locate and control populations. They will also replace money in much the same way as a credit card replaces money.
I agree with kentuckslone, money will always eist and in the event that it does not, it will probably be exchanged for something else. Some might even believe that we might actually revert back to the barter system.