User blog comment:LilyheartsLightning/Citadel and Reckoning DLC announced/@comment-3046679-20130221180207/@comment-24174486-20130221193413

You can't pause a multiplayer game. =^_^=

And Lancer, if they do add a Horde Mode of sorts with the Combat Arena, it'll be alongside the story content that they're including. They can add combat-based additions alongside story content, as they appear to be doing with Citadel and the Armax Combat Arena.