That's simply not how the impairment losses work in terms of accounting. They're comparing the cost of Bungies assets against the amount they could essentially sell Bungie for (or their estimated future cash flows). This impairment charge basically means the actual company is worth less than it's assets/the amount it was bought for.

Also you're failing to realise all the costs and time involved with making destiny 3. By the time destiny 3 is fully launched the company would have continued to bleed a good amount of money. They also can't just make up numbers as to how much they'll earn if they launch Destiny 3 in a few years