I was about 90 seconds from leaving work last night for our office holiday party when my editor walked up and said, "John Spencer died." After a minute to process this, Matt started working the phones while I began looking for archival quotes so we could write the obituary.
John Spencer was one of the nicest celebrities I've ever had the pleasure to meet. He always considered his post-rehab life to be time he hadn't expected to have, so while 58 is way too young to die, he enjoyed every damn minute of the last 16 years.
It's obviously much too early to know what "West Wing" is going to do without him. The show caught a bizarre lucky break when Leo wasn't included in the flash-forward to the dedication of the Bartlet presidential library in the season premiere. At the time, I heard lots of speculation about his absence: Leo's busy doing some VP assignment; Leo is actually the president (Santos having died sometime after winning the election) and is therefore the guy coming out of the limo; Leo suffered another heart attack and died. I'm almost certain they have to kill him now; the only question is how close production was to the election episode.
About the only silver lining of this whole situation is that it could spur Sorkin and Schlamme to come back to write and direct Leo's farewell. Hell, if we're really close to the end of the series, maybe Santos chooses a familiar face to be Leo's replacement: Sam Seaborn.