At the following
LINK is a thread on this forums where Raze reposted a quote from someone in Larian about what the Blessing Ceremony and the last cutscene meant. I think it would answer your question of what happens in the last cutscene.
As for the last Diary message, I never saw one or even heard of one, as killing the Demon of Lies gives you the last cutscene, then I believe the credits screen, and lastly puts you back at the main menu. So all you're missing is seeing the last cutscene. I'd assume there's some way to watch it without killing the Demon of Lies again, but I don't know which file on the CD is needed, nor what program would be used to open it.
Oh, and as for the game freezing after killing the Demon of Lies, I'm not quite sure but that sounds to me like how the program behaves when it looks for the Blessing cinematic or the Ending cinematic without the proper disc in the drive.