As it turned out, my report of the death of Cosmos-2422 early-warning satellite was an exaggeration - the satellite is alive and well. It did behave a little bit unusual, not performing station-keeping maneuvers between August 2009 and May 2010, but it has been performing well since then.
This means that the early-warning constellation includes one more satellite than I thought it did when I was reporting on its status in April 2010 and then in September 2010. There are four operational satellites on highly-elliptical orbits now. No geostationary satellites are operating, though.