When the game goes live and out in the real world. Per a post it was stated that the retail box version 1.00 will have absolutely NO DRM on it at all. You can put it in and play, without ever updating it.
Once you've got the game updated though, you do NOT have to be connected to the internet to play (excepting obvious MP games against others on said internet).
And also you do NOT have to keep Impulse up and running, or connected all the time. This isn't Steam and they don't want YOU the customer to have a bad experience.
It's just the beta right now they need a connection from what I've gathered. That's it though.