^ I don't know, their words and this being a HOTFIX, seems to think it wasn't cleanly planned out as you allude to, they decided as it happened:
Many of you may have noticed that the Cataclysm content is… well… not totally gone. Technically, the Cataclysm event has officially ended, as planned. However, the team decided to leave some of the elements for you to play until the next content release. With that in mind, here’s what we’ve decided to leave open until the next seasonal update:
The Echoes of Reality portion of the Cataclysm will remain open for you to enjoy
You will still retain and earn Crystals in the EoR runs
With that said, we know we have some various UI bugs we did not anticipate. The team is working to resolve these. Here are the details you should know:
We’ll bring back the Seasonal Store later this week, so you can spend the remaining Crystals you have, while you continue to earn them in the content still in the live game.
Second (and this one is important), your Crystals will not carry over to the next Seasonal Event.
Finally, Daily Cataclysm Challenges, Story Missions, and Freeplay Events will not remain. Leaderboards will be visible for now, but will not be updated and remain blank until the next event.
We’re not ready to give a date on the next content update yet, but stay tuned and enjoy the Echoes of Reality map until then.