Well, I guess there a number of different directions this could could go in. I'll try to share some thoughts from our experience building Ajax user interfaces for large businesses and relate that to Java.
First I don't think Java is going away anytime soon. In fact over 1/2 of the customers we serve (and they range across the world, industries and headcounts) are using Java in some flavor on the back end. One of the problems is there are so many different technologies and frameworks that fall under the Java umbrella: Java, POJO, JSP, Servlets, Struts, JSF, Spring, Hibernate, J2EE...just to rattle off a few. Let's not even get into app and web servers. But needless to say Java is going to be living on the server for a _long_ time.
As front end/ui technology for the web though I would have to say it's all but dead. Java applets never really delivered on their promise. Developing the UI layer of a web app through HTML and Ajax talking to Java on the server side makes a lot more from a user adoption point of view. The ability to run an Ajax UI in almost any web browser while providing a rich and satisfying user experience is really what makes it king.
I think I could ramble on forever here so I'll just let you ask more specific questions if you have any