From the West Ham website:
Hackney Wick Station has limited capacity and will not be available on match days;
Read more at http://www.whufc.com/new-stadium/about/location#CyLJB0U2OlsiYY6y.99
Train to Waterloo for me and then Jubilee Line to Stratford. Last train home is 01:05 but I hope is doesn't come to that. I could go back to Waterloo on Central Line / Northern Line but I don't suppose it makes any difference.