There's only one thing you can do. Ask for free stuff. The ladder is finished already anyway. In a mere few weeks there will be a reset, so maybe some generous guys can give you the stuff you lost for free. But
But maybe you're lucky since i found this in the server rules:
► Show Spoiler
We won’t do any rollbacks unless it was caused unambiguously/clearly/provably by some server error
If it really was a server issue, maybe the admins are willing to do a rollback. Try messaging Aahz.
In order to prevent something like this from happening in the future, only mule via trade window. That way you won't lose anything ever even when a DC happens.