When an account is in memorial state the account holder should be able to log in, her account then should change automatically into normal state without any administrator approval, and she should be able to prohibit her freinds to put her account into memorial state again (with a checkbox).
As she is the only person who may know her password it is not logical not to allow her to log in.
I don't think that when the account holder logs in that it should automatically revert. It's more than possible spouses etc. would have a dearly departed's password.
But they should certainly still be able to log in, and once logged in have the option to recover back from memorial mode - without needing to go through support.
Edit: Also, it would be nice to have a feature where I can nominate an "in case of emergency" contact that, if my account falls into memorial mode, they will then gain access to it... to maybe post a little more info about what happened, or contact friends that they might not necessarily know themselves, but would like to invite to the funeral?
Perhaps arrogantly, but I believe that if it happens when we still care in any way about our Facebook accounts - and not the next big thing - then I imagine that it will be upsetting for my friends and family, and I care now that it is as easy on them as possible.