“- Growl is not dead – Growl is alive and kicking – We are still actively working on shipping two future versions of Growl. Our understanding from press reports at this point is that Notification Center is only available to apps from the Mac App Store, which effectively locks out the entire class of applications that aren’t or can’t be in the store.”
Seems reasonable. I hope they won’t go away but if the Notifications API ever goes “public” for all applications, AppStore or not, Growl will find themselves between a rock and a hard place.