So if they're 20,000 light years away and they can travel at the speed of light to check out who sent the message they could be on our doorstep wiping us out in 40,000 years.
I say go for it! Our descendants will barely remember that we existed anyway.
Just because it isnt possible now with out current level of technology doesnt mean it isnt possible.
There is something between isolated particle theory and gravitational drives here that applies...but that is instinctual...I am no scientist.
I firmly think the key to faster that light travel is unlocking the mystery of gravity's effect on local space time.
The energy required to break away from local space time and the gravity well must be enormous.
Dare I say it....God like.