Guys, calm down, this thread is over. Mr Nice your answer to your question has already been given already, please read through the thread if needed, I at least know my post pretty much captures it completely. However I will go ahead and indulge in this little exercise and break down possible issues with the cans and who can fix it/what you can do as an owner.
(1) One/both of the drivers go bad and need replacement.
Only Joe can help you, as he is the only one that has drivers. Again the issue will be what happens to his estate, does it go to John or someone else, only time will tell, and hopefully we won't have to answer that question for a very long time, bless his wonderful soul.
(2) Sound does not come out of a particular channel, but the drivers are still operational.
This has actually happened to me and is very easy and cheap to fix. Basically one of the wires that connects to the driver can sometimes snap off due to pressure or old solder joint. All you do is have someone willing able open up the cans and solder back on the wire to the voice coil pad. This happened to my 1st set, I sent it to Larry from headphile, he charged me I think $25 for 1/2 hour of labor and shipping, and they worked perfectly. Word on the underground was that this happened to jpelg's set as well but thought the drivers were dead and for some reason had John replace the drivers with RS-1 drivers. I believe someone snagged up those perfectly operational HP-1000 drivers within minutes from John.
Now if its not just the wires but the whole voice coil pad disattached from the driver then you are screwed. Refer to option 1.
(3) No sound as a result of a cable issue.
Very easily fixed and repaired by numerous users, go with one you are comfortable with and experienced with. Based on my experience I would probably go with larry from headphile. However you will not be able to get the original Grado cable unless you cannablize something else as Joe no longer has them according to one of the previous posts.
I think that is about it Mr Nice in terms of possible issues and areas to fix them. Its pretty self explanatory and doesnt take too much to have figured that out on your own. I am pretty sure your question is more than answered so lets please move on, thread over