Each tub I've ever had of creatine has had an expiry date on it so I a.ssume it can go bad or that wouldn't be needed.
Also keep in mind that it can go bad if you let it sit in water or juice too long. When you do so, it goes through degradation and turns into I believe creatinine which basically is no good for you and you probably will end up just pissing it out. However, I've been communicating with a few different companies in regard to their creatine products and they are stating that that process is rather slow and it's been completely blow out of proportion but the general public who think you have less than an hour to down your creatine. However, that doesn't mean you can mix a weeks worth and let it sit for the entire week. Myself, I drink my creatine supplements intra or post workout and make sure to keep it to about 5g's a day unless you are going through your loading phase.