It would take the star's light (or other radiation, like heat) that long to reach us. The star itself is going much slower than light. For instance, it takes the Sun's light about eight minutes to reach Earth, but it takes many months or even years for a spacecraft to travel that distance. It's all a question of speed.

So if a star is 7 light years away, that means it takes light seven years to get to us from that star, and since light always travels at about 186,000 miles per second, that means the star is about 5,869,713,600,000 miles away. (Assuming I've done my math right. ) Even at the velocity of our fastest spacecraft, Voyager 2, it'll take an incredibly long time to travel that distance. Light years are very very very long distances. That's why interstellar probes are still a pipe dream. It's just a phenomenally huge amount of distance to cover.

So even if there was an object at that distance travelling on a collision course with Earth, I wouldn't worry too much. Our great-great-great-great-great-great-great-great-great-great-great-grandchildren won't even have to worry, really.