How could Voyager navigate inside the starless void? Especially since it was very large. Taking one year to cross. Some sort of inertial navigation maybe?
Voyager's navigational computer was able to calculate it's relative distance from Earth from the very first moment it was in the Delta Quadrant (70 thousand light-years). Not only that, but the amount of times Janeway told Paris to 're-set a course for home' (after having made a detour or three), makes it seem that such a distance could be plotted fairly quickly.
Their trip home was originally estimated at around 75 years. This was based on both the ship's speed, and the distance from home. Knowing this, one year's worth of 'Starless void' would seem like nothing for the navigational computer to plot a course through. All they would have to do is pick a point or two on the other side of the void, and constantly measure distance and heading from those points, to make sure they kept on a steady track.