For the record, the previously reported figure was
320k EGS copies sold, on the second week after release.
That means there were 380k EGS copies sold since. Assuming AMD promo copies are excluded, and given that the last figures as of a month ago was
"nearly two million players", I think it would be reasonable to assume that the bulk of these EGS copies was purchased during the MegaSale.
Napkin maths time:
1) Assuming that World War Z has exceeded the sales guarantee/repaid the advance, and is getting charged the 12% store fee,
2) assuming that 75% of the 380k sales were made during the Megasale (so, 285k), and
3) assuming all of these 285k sales were US sales (again, napkin maths!)
Epic was losing $10 - $3.60 = $6.4 for each copy sold during the Mega Sale
Which means that we can estimate that Epic lost $1.824 million dollars on World War Z alone during the Mega Sale.
This is not sustainable in the slightest.
The punchline: this is probably an underestimate. Since the Mega Sale was a fixed $10 discount on any game priced $15 or higher, Epic's losses would have been greater the cheaper the Mega Sale price was.