It is widely known that "World War Z" basically retooled and re-shot its entire third act at considerable expense to the studio.
MINOR SPOILERS AHEAD
As previously revealed, the switch over point takes place when Brad Pitt's character Gerry and injured officer Segen board the plane to get out of Jerusalem as the zombies over run it.
In the earlier version there was an elaborate and large-scale battle set in Russia. In the theatrical cut, we get a fairly suspenseful mid-air sequence followed by a third act almost entirely self-contained within a Welsh medical facility.
Now, Movies.Com have done an extensive write-up of that earlier version's third act based on a copy of the screenplay that was used at the time before the retooling. Not all, but a good portion of this was actually shot. Click the link for the quite in-depth summary with all the juicy details. For those who don't have the time, here's the quick breakdown:
The plane, bound for Moscow, safely lands. All but the healthy people are executed, those who aren't are drafted into service and Gerry's phone is taken. Months later, a now bearded Gerry has become an efficient member of Russia's zombie-clearing squad who are now tasked with clearing the capital's subway tunnels.
Using Lobos (a zombie killing tool from the book), the team make their way through, only to emerge above ground into the "Battle of Red Square" which is described as a much larger set piece than the Israel scenes. Gerry and his new British friend Simon head back into the tunnels where Gerry figures out the zombies are having an extremely difficult time with the Russian winter.
They try to inform the Russian command to extinguish their fires and let the undead freeze. They also meet up again with Segen who is in the clutches of a rape-friendly Russian soldier. Saving her, Gerry gets to a Russian general and is able to turn the tide of battle. As things quieten down, he calls his wife.
Turns out the wife is stuck in a refugee camp in the Everglades where she's been forced to be the reluctant love slave of the soldier (Matthew Fox) who rescued them from the rooftop in the early scenes. He warns Gerry to start a new life, Gerry does not and sets out with Simon and Segen across eastern Russia until they find a boat and head for the Oregon coast in a fierce effort to get his wife back.