One by One
The vampire settlement had their own fleet of ships and different types. They often used them to explore the planets in their solar system and in case there were other needs. However, the spaceships were never meant to be used in a war.
The vampires never planned a full-scale evacuation because the settlement was their safe haven. If all of the vampires were to up and leave at once, then there wouldn't even be enough space for all of them.
Thankfully though, there was enough room for them. The vampires might have found the ships cramped for them, but they realised that there was space for them, and that was because a lot of the vampires were dead. Those vampires had gone to the war and sacrificed themselves, while many died due to the infighting from before.