This isn't the only case I've heard of this - I remember reading about one study referenced in a book by Richard Wiseman, which showed that the number of people who pass away in hospitals rises significantly after times like Christmas or (on a more individual basis) a grandchild/loved one's birthday. People seem to be able to "hang on" to some degree or another for brief lengths of time.
On a more personal note, I remember when my grandfather was in a hospice, the nurse told me that she could tell which patients would soon pass because they had embraced it and stopped resisting it.
I'd also like to say I found this post very moving and I'd like to express my sincere condolences for the loss of your friend. It sounds like the two of you were very close.