Argh! No!

One of my Gamecube memory card's data has vanished!! :cry: 

It had like 400+ hours of Gameplay on it :evil: Looks like I'll be redoing Tales of Symphonia, Super Smash Bros. Melee (unlocking EVERYTHING), Final Fantasy Chrystal Chronicals and wait for it...

Animal Crossing! :cry::cry::cry:

Has this happened to anyone else before and while I highly appriciate it if anyone knew any possible ways to retrieve data, which is probably most unlikely...