The BitMEX EOS Token / Bitcoin 28 July 2017 futures contract, EOSN17, will expire using the .EOSXBT30M Index. That index will use the price observed on Kraken.
The BitMEX Status Token / Bitcoin 28 July 2017 futures contract, SNTN17, will expire using the .SNTXBT30M Index. That index will use the price observed on Bittrex.