Alot is so nebulous. I can also say with confidence that alot of "4E people" merely prefer the edition over 3.5E and if left with no new content for 4E might "move on" to a supported version (Pathfinder). I believe that D&D has remained at the top of the RPG world for one main reason: support.
In principle, a 3PP such as a Goodman or Mongoose (or somebody else) could step in and produce new titles for the "4E refugees" crowd in the event that D&D is completely taken off the market. One could argue whether such a gesture is just a "last gasp" or "too little too late".