Yes it is because we hear him say something like "Humanity stands as the greatest threat on the galaxy- And now we have this fate we are forced to recede-. Reclamation has already begun, and we wish to stop it." That's all referring to current events. Humanity is the greatest threat in 2557, and the Didact couldn't talk about his punishment because he was unconscious when he was placed in the Cryptum. And the thing that confirms it is the last sentence "Reclamation has already begun, and we wish to stop it." Humanity has begun to rise up and reclaim the mantle, so he is owing to try and stop it, again.so yes, the epilogue does confirm the Didact is alive.