APOCALYPSE NOW, BUT NOT SO BAD LATER
One of the central areas of interest for ZRS is the Zombie lifespan. The theory being that if a rough threat time line can be established – starting with reanimation, and ending with decomposition – then strategies and expectations can be adjusted accordingly, resulting in millions of lives saved.
It’s already been asserted that Zombies can only be up and walking in the first stage of decay (see: Fresh Stage Decay & The Zombie Lifespan). 
Once the body reaches Bloat, the brain has liquefied to the consistency of New England clam chowder. Unfortunately, because the rate of decay could be significantly slowed in the undead, the Fresh stage may not last just days as in human, but months, years, or even decades. George Romero’s Land of the Dead suggests as much.
One thing is for certain: If Zombies don’t take a considerably longer time to rot than their deceased human counterparts, we may be in much less trouble when the undead rise than originally thought. Especially if it spreads very quickly.
Assuming that Fresh stage decay takes two weeks to complete, it’s likely that by five weeks after outbreak there would be virtually no more Zombies anywhere. All you’d need to do is hide out in a safe place with enough food and water for a month, and you could emerge the leader of a new world.
Of course, if you’ve miscalculated and it’s longer, you might just find yourself in a pretty ugly spot once the rations run out and you don’t have an adequate escape plan.
How long do you think is the Zombie lifespan?
well, to find out how long the decomp. time is, lets look at the Colony of Roanoke(1587-1590)
assuming that the colony was overtaken by an undead scourge then the decomp. time would be as much as 2 yrs assuming that the infection is isolated and no further living targets enter the area.
That’s a great idea! Look for a post on this coming soon.
Yes, I’ve done a lot of research on the body farm, and love Mary Roach’s bestseller, STIFF, which includes much information on decay, and many body farm references.
Depends on a lot of factors, if there is no microbiological agents of decay because of the zombie virus, they could last for years, also climate. In the arctic or a desert environment they could last for years. In the tropics or by the ocean, it would be a lot less. You might wander over to one of the body farm web pages to see what happens to normal bodies left lying around.
http://en.wikipedia.org/wiki/Body_Farm