Comment by jandrese

More to the point the ship needs to be absolutely self sufficient, it can't even use solar power and has no access to outside mass whatsoever. But if you have a ship like this you could build an orbital habitat using the same technology, and it would be much much easier to build since it doesn't have to accelerate, can use solar power, and has access to the rest of the resources of a solar system.

If you have all of this why would you go to the enormous extra effort to move the habitat to a different solar system? Even if your civilization is so old that the star is a dim brown dwarf that's still plenty of energy for day to day life.