As we are obviously under the assumption that zombies are possible, I will start without going after that. While I didn't read the whole synopsis, (thus obviously haven't read the movie) can the zombies swim hundreds of kilometres to an island in the middle of nowhere? If they apparently can, it's on. In order for objects to move, they must have either mechanical or biological propulsion. To cut to the chase, zombies have to eat. With 99% of the world zombies, they would have to eat each other as farms would no longer produce food. In this sense, you could out last the zombies as they would not be able to sustain themselves with animals. They couldn't run around forever, as energy is conserved, being able to move around requires energy. So unless they made a huge efficient mass of zombies move towards the island, assuming they were intelligent enough to take one for the team and get eaten for the cause of whatever it is their cause is, assuming they somehow could sense humans,(direction to swim) and ate one another to keep going, thus reducing their assault numbers significantly, it would be impossible to attack people on an abandoned island in the middle of the ocean. As for supplies running out, that would depend on the islands size and the number of people there and their individual food and water requirements. If they were only in a fortress, that would pose a problem. Although, they could just run around outside gathering food, if humanity still has the capacity to fend for itself, that is. As for zombies outside, that would depend on the population in such an area. I did read a bit at the end of the synopsis that they planned to drive to Canada. Zombies would not be able to follow you far north, especially if the infection was in winter. Assuming zombies aren't intelligent enough to bundle up, they would die very quickly to freezing temperatures. If you were with a few companions armed with good guns and lots of ammunition at the top of a Canadian mountain in winter with a three weeks worth of supplies, you'd be fine. You can survive without food for three weeks, so if the zombies didn't eat each other, in three weeks they would all be gone. If they did, well, the disgusting mathematical fun begins. I have decided to remove the research I did on calories per unit of human flesh, (no one seems to be well learned on the subject for some reason) and simply say that humans have an average of 50000 calories, and that one zombie would have to be sacrificed to twenty zombies everyday. Since they are brain dead they would likely use their collective resources extrememly quickly like humans and end up all dead in slightly more then three weeks, but let us assume they do what I say for now. If we take New York, a city of 8 million (ignoring the minus 1% since it's a rough number) the zombies existence would have an extension of (I can't remember what equation to use) days on the 3 week starvation threshold, thus making New York zombie free within under 100(lets say) days. While there would surely be other food sources to increase their existence, let's say the zombies eat them first, granting them another, say ten days on their existence. In conclusion, you could ride out the zombie storm. And I hate zombie movies, fyi.
