Testing this I noted that you must have planets that are with in view (via) warpoints to maintain contact with another race. I gave away all my planets to my opponent and lost contact with him even though I had a empty colony ship.
This empty colony ship was a powerful weapon though. I colonized a planet with it and then the next turn I was dead but I took away the planet as well without leaving any asteroids behind.
Looks like I will be submitting a bug report to MM on this one
