Supposedly there are 1.7 subs, so I think there are plenty of people still playing. http://latimesblogs.latimes.com/entertainmentnewsbuzz/2012/02/star-wars-the-old-republic-snags-17-million-subscribers.html
That's as of December 31st, i.e. every one of those 1.7 million subscribers are still on the first month that is included with the game. It'll be interesting to see where the numbers are at March 31st.