So do they just maintain their initial velocity or would we have a chance to discover the static reference velocity of the universe?
Also they would still be affected by gravity if they still exist in space. Gravity is not a force that pulls objects together. It is merely the act of going straight in curved space. Either they are in that space and they are going to move along it within the shape of that space or they are not in that space. Though really if they just moved in a straight line with no external forces they are going to be subterranean because a real straight line in our space is down.