If there is an observer, like maybe a "god of time," for whom:
our temporal dimension is his fourth spatial dimension;
the relationship between successive timelines is his temporal dimension -
- then, from his perspective though not from ours, our timeline has vanished.
The blurb concludes by stating that the past must not be altered in case this leads to a worse future. But, even if it led to a better future, the Danellians would still guard the timeline that leads to them. However, it transpires that ultimately the Patrol prevents a worse, chaotic, timeline in which life would be impossible.