From the best I can tell there are a lot of us still waiting to hear from the CS department with respect to masters program admissions. I personally plan on waiting them out, but if you are under deadlines it probably wouldn't hurt to try and contact them. I'm not sure what the policy is about asking for an extension from the other Unis.
I know that it has been brought up elsewhere about accepting and then declining admissions at a Uni and it is pretty frowned upon and may have some negative repercussions.
