I was a bit worried because while cleaning my food cabinet I found out that I still had the bottle of champagne I won in a competition several years ago. Taking a lucky guess, I would say champagne, just like wine, is made out of grapes, and therefore the longer you keep it, the better it would taste. My hypothesis can be wrong, so lets leave it to the experts.
What experts say:
* Your wine will not expire for many years if kept in a cool dark place -- but it will change slowly. Some people think that this change in flavor is beneficial, others prefer Champagne fresh.
* As long as they are left unopened, they will be fine for years.
* Stored properly, champagne will be fine for 3-4 years, but may begin to deteriorate if kept longer. Some champagnes retain their quality even after being stored 10 years or more, but it is not recommended.
So I'm guessing it is fine to keep champagne for a few years, depending on the brand and make. I guess the best way to find out is open it, see if it smells/tastes fine, and if I don't end up with a bad stomach ache then I guess its all good!