We have done a rough calc of what the MERC guild attack cost us. We may never get our cost back but we can ensure that MERC does not profit off us either.
As a secondary bonus, we also can demonstrate we are not a guild that makes idle threats to those who wrong us.
As previously mentioned, we can also ensure any contracts accepted by MERC in the future against us will command such a high price, their customer will have to cough up hundreds of millions to allow MERC to earn a profit from it.
To be honest tho, I am enjoying a guild war that there is far too few of these days. Just throwing money into nation wars is usually such a predictable outcome and not a lot of in-guild teamwork involved.