Yes, you can drink 30 year old champagne if it has been properly stored. Sparkling wines such as champagne gain complexity and finesse with age, becoming more mellow and rounded by the time they reach their maturation date. But there is a caveat to this – provided that the bottle of 30 year old champagne has been kept in ideal conditions.
Ideally, your bottle should have been kept in an appropriate temperature (ideally around 12-14˚C). The humidity should also be monitored closely so that the cork does not dry out; wine corks are hygroscopic in nature and will easily absorb dampness from humid air or leak moisture into dry environments. Bottles stored upright will ensure that any sediment formed during aging stays at the bottom of the container until it’s served, however bottles should be frequently rotated to prevent uneven shelf life after opening as well as ensure good fill levels for further storage before drinking.
In short - yes you can certainly drink 30 year old champagne if properly cared for! As long as all of these parameters have been followed correctly then those aged champagnes are guaranteed to offer excellent flavour profiles; however if uncertain about its condition then it’s best to err on the side of caution and taste small amounts first before consuming larger quantities!