The HP Slate is NOT dead! It is just in the process of a major re-vamping. TechEye reports that HP has announced that Windows 7 will not be the OS for the HP Slate tablet. They haven't confirmed that webOS will be replacing it, but their acquisition of Palm makes that a foregone conclusion.
HP's main issue with Windows 7 is centered around battery life. The Slate was rumored to get around 6 hours off of a charge, fine for a laptop but far too little to compete with the iPad. WebOS ought to add at least an hour or two to that. Plus, there are rumors that HP will be dropping the Intel processor for something a little less power hungry.