A post on the Steam forums suggests that ringing up EA’s support lines to complain about the untimely demise of APB might be fruitful. The poster in this instance managed to get 4000 Bioware points, which I think is about $50. Worth a shot, if you’re glum about your APB purchase, anyway.
It’ll be interesting to see whether the game gets resurrected long-term, as has been suggested in a number of rumours, and whether that will attract the original purchasers of the game. Personally, I suspect it will stay dead.
More on refunds here.