Google Wave may be going away, but it is highly unlikely that the web has felt its presence for the last time. As Google said in its announcement, the company will extend the technology for use in other Google projects.
It will be interesting to see if the technology still goes by the name Wave, but I have little doubt that some of the innovations we've seen in Wave will be popping up in various Google offerings in the form of new products and new features to existing products.
Google's aim with Wave was to replace email. That didn't happen, and frankly, I have a hard time believing that too many people bought into that one, but that didn't change the fact that Wave did some interesting things. One only had to watch a demo or two from someone who knew what they were doing to see its potential.