It still is (release May 2009), so I would say much longer than Red Orchestra.
I admit I was being a bit childish with that, but comparing the lifecycle of the first game to the sequel is not really the best thing to do, especially considering the REALLY goofy launch RO2 got. Not every development cycle is set like CoD or Battlefield.
I'm guessing Tripwire will possibly be doing background work on RO2 while focusing on Killing Floor 2, while AMG will, I guess, be doing the majority of the work on RO2.
Then again without solid information from the devs themselves we can only guess at stuff. I'll just be happy to have the number of tanks expanded even slightly. Heck, the more they do it, the better they will (theoretically) get at it so any additional vehicles added may have a faster turn around.