You can drive without the sway bar, but don't drive too fast, and take curves and turns exceptionally slow. Take off the endlinks if they are just hanging loose.
If you go to the dealership, familiarize yourself with this case:
http://www.impalaclub.com/naisso/magmoss.htm
Basically, the dealership has to prove that the aftermarket part: the Eibach springs in this case, caused the sway bar to fail.
Although the springs and the sway bar are related suspension items, it does not mean they caused it to fail. I'm not sure how this case would play out if the item was already prone to failure. If the 08 sway bars are under recall as el_blacky06 said - you're in good shape. Eibach springs should not cause a defect-free stock sway bar to fail. I would call Nissan Consumer Affairs and see if they can send you a new one without having to step foot into a dealership. They might do it if this is a known issue, but they might want a Nissan dealer to install it. I'd say it's worth a try.
If you have $150 to spend, I would suggest going with a Racingline sway bar. It has two adjustable settings.
The stock sway bar sells for about $100. I still have my stock one just taking up space, and I can let it go for real cheap. If you're interested, shoot me a PM.