If floppies are kept in ideal conditions, they can last a good many years. But the exact amount of time they will last really depends on way too many variables to calculate. Generally speaking, like most things, the better the material used to construct things, the longer it will last.
One other thing... Magnetic based media like hard drives and floppies are disks. Optical based media like CDs and DVDs are discs. Don't ask me why they needed two spellings, I think it's stupid too.
I own a never-opened copy of Ultima VII Complete Edition (purchased in 1992). It's a collector's item in that the box contains all four parts of U7 as well as the original cloth maps, trinkets, etc. The problem is that the game is on floppy discs. What are the chances that, after 12 years, the data would still be intact to allow installation of the game? Thanks.