Olly Smith wrote in the Live Mag (Mail on Sunday) in answer to this question,..
Will Champagne be OK after two years unopened?
Yes, it should be fine. It's one of the few types of wine that can be stored upright rather than on its side and even non-vintage Champagne develpos more savoury depth over time. He goes on to say that he has tasted champers from the Pol Roger cellars from WW1 and that it was still in good condition with some bubbles and and it was very ruch and savoury.
Can't imagine anything with alcohol lasting for 8 years in our house. * mins possibly