Same thing happened with Verge last year. An online wallet verge-wallet.xyz just disappeared from the web with all coins stored in there. ( I personally lost 10k verge stored there).
After a while the price started dumping till it reached 53 satoshi. Apparently, when the site owner started selling what he stole.
Then after months, the price started moving up again.
So it is a matter of time, I think, before xem price goes down and the stolen coins be for sale.