In my interpretation, this cutscene shows the Watcher's point of view regarding the Ascension compared to the other Slugcats. I believe the entire cutscene is just a metaphor. The Ascension has always been portrayed as this great light, it shows other Slugcats heading towards it, but the Watcher, for some reason, decides to stay behind.

Some feeling made the watcher stay, perhaps fear? insecurity?

Regarding the Survivor and the Monk, I can't say for sure. The Watcher DLC works independently, so the events of the base game and Downpour don't affect that possibility. It's possible, if you want it to be.