See the story on CNN
He was such a reliable presence for me every Sunday morning as the host of Meet the Press since 1991. With so much changing over a short period of time, he was a constant for a very long time.
Few newscasters ever had as much research ready when interviewing political figures all over the world, and communicated it very clearly. He always knew where to find the pressure points of his guests and press them to the limit with very hard and proven facts. Whoever replaces him will have a very hard time performing with the same quality and knowledge.
It sounds like he overworked himself to death at a very young age. However he died doing something he loved a lot, so you might say he was blessed.