The mod version of Better Questing - Quest Book that the pack uses doesn't exist anymore on curse.
I suggest updating to an existing one.

I'm fairly sure it's not a problem currently, might have been some curse thing, or has been fixed.

The pack in 1.2.1 uses Better Questing v3.5.300. Sometimes the download servers have issues and a mod will fail to download, but it would be very unusual for a mod to just completely disappear.

Whoops, BQ-QB not BQ. You're right, it does appear that there's no listing on curseforge for that file anymore. Somehow the launchers are still able to get it, however.

We should switch over to 3.1.1-1.12 for the next pack update.