I'm sorry to hear about the other egg not making it. :(
Be sure to post some pics up when it does start getting some feathers. Most of us here just love looking at them. ;)
Congratulations on the new baby!
Anytime 2 different breeds cross it is a hybrid. Muscovies and Mallard based ducks are capable of crossing, however it will be a mule. Likely a very beautiful mule though. Could you post a pic? :)