"In 2012, rumors began circulating on the Iranian Internet that Pepsi planned to use powerful lasers to shine the image of their logo on the Moon’s surface. Thousands of Iranians climbed onto their roofs to stare at the Moon. When nothing happened, some bought Coca-Cola out of spite."
It should be used within a month. If in an airtight, properly sealed container it might last up to six months, but it will still separate and become grainy and slushy and won't taste very good. After that, bacteria can start to grow, even in freezing temperatures. Life, uh, finds a way...