Here's the flip side.
1,700,000 x 15 x 12 + 2,000,000 x 50 = 306,000,000 + 100,000,000 = $406,000,000
Development Cost: ~$200,000,000
Profit: ~$206,000,000, I'm sure BW is feeling just fine More is always better, but it is pretty much a sure thing this game will turn a profit at this point.
On a side note, the point about retention rate is very valid. Every game will shed subscribers from the initial influx in the first few months. More important will be the rate at which new subscribers are added as the game matures.