We all know that when you delete your facebook account, it still exists within their servers but the reasons why that make sense (i.e. in case you want to come back, their data using purposes) are not as applicable if you've passed away.
So there is the question of ownership. For example, could your family request control of your account? I'd rather this than facebook or my account sitting idle but then again, if you haven't consented to it, that doesn't seem right.
There is also the question of your footprint. Does facebook delete your account on your behalf (assuming they are notified) or does it just sit there like a virtual tombstone?
Finally there is the question of information. Assuming facebook knows about your passing ans deletes your account, do they still hold that information in their servers as they do with other people who have deleted their accounts?
I've had friends who've passed away, and their facebook is still up; people write messages on their wall every once in a while saying that they miss them and so forth, so in a sense, it becomes like a virtual memorial. I've also read stories about families that wanted their deceased relative's facebook account deleted, but they didn't know any of the security questions or other information, so Facebook wouldn't delete it.
I think a good solution would be for Facebook to automatically deactivate (but not delete) your account if you haven't logged in for a year. Thus, if you ever go away for a while, forget about your account, etc. it will be there when you get back, but if you've died, it's automatically removed (in a sense).