Man, Wonderful example of dignity!
30 million euros is a lot of money, but I was thinking... I think this casino will earn much more on the long run for honor winnings instead of voiding bets.
You said this bug attracted many new players just to exploit the flaw, right? Now imagine how many of this players stayed in the platform after seeing that it was honored?
Of course, a 30 million euro of "forced marketing" is quite expensive but I believe the exchange must have partnered with Playtech (which is also a giant company) to offset this loss together.

For me, this case serves as a benchmark for other casinos... that transparency and accountability are much more important than a partial loss when the error comes from the casino itself.