I'm pretty sure they're dead, mate. Face it, they were surrounded by zombies on the moon. And Richtofen is now controlling the zombies. If they were still alive, they would be doing other things than sending morse code to a blown up planet.
I still believe this whole easteregg/storyline so far is going to base on traveling back to the point where the zombie apocalypse started. That's right... time travel. Richtofen wants to 'save' his planet, and the only way to do that is to travel back to the point before the original four, by Dr.Maxis help, blow up Earth.
The morse code is some clue that there are other survivors though. Not necessarily the original characters.. actually, DEFINITELY not! Where would they send it from? They were stranded on Moon filled with the undead, dood! As much as I want to believe that they are, I'm pretty sure they're not.