Yesterday when the news came out that Monty Python member Terry Jones had passed, fellow member John Cleese tweeted "Two Down, Four To Go." I think Terry Gilliam tweeted the same line.
A number of folks posting online have said that they thought this was an insensitive thing to say/tweet. No. As others are pointing out, it was just the continuance of an ongoing joke the Pythons started when they subtitled their final performances (the ones at the O2 in London), "One Down, Five To Go." See it there on the banner?
When either Cleese, Gilliam, Idle or Palin dies, one or all of the others will post or proclaim, "Three Down, Three To Go" and so on. When the last of them joins the bleeding Choir Invisible, someone will tweet, "Six Down, Zero to Go." If the Python guys know anything, they know how to pay off a running gag. I suspect each of them would be hurt if their survivors didn't keep it going.