KuMEX never went offline even though you can attest to say that the exchange doesn't have any recorded volume of trades. Actually, KuMEX was merged into the KuCoin exchange which apparently, were the ones who developed the exchange. KuMEX which was primarily focused on Derivatives and leveraged options centered on that area for a long time and then following KuCoin launch, they got merged and closed. KuMEX still maintains all of its inherent prowess of a derivatives exchange within KuCoin, operating under a separate fraction of the exchange, with it's very own wallet and options. It was never closed, just simply merged. If you want to use KuMEX then you can head out to KuCoin and get it to do your biddings