After I captured the wizard guy and brought him back, they didn't give me another quest, though I noticed Astryl's Tranquility opened up. When I went over there though, it took me to the winter Festival explore zone. Have I reached the end of the current storyline?

The storyline continues in Astryl's Vale. However, since the festival zone is considered part of that region, you'll have to exit it in order to go to the other zones in Astryl's Vale. That's how the 3rd region works. If you want to switch within zones in the 3rd region, you'll have to exit the one you're in.

If you exit though, you'll lose any "progress", which means you'll start at the beginning of the zone again. For the festival zone, this also means you'll reset all spawn times for presents/bosses.

Okay! thanks :)