Now getting legal advice, I've been told that proving there was a fraud would be very difficult, unless having access to Poloniex's whole data, but there was definitely a mistake. Things like this, that CLAM crash because of crazy margin trading, should never happen.
I wouldn't think fraud would be the angle here. Something like negligence with regard to capital and margin requirements, maybe.
Does anyone know what jurisdiction this case would fall under? Did the lawyer you spoke to say? As a US company, capital and margin requirements would normally be covered by CFTC regulations. Since US persons aren't allowed to lend or margin trade on Poloniex, I'm not sure they apply here.