If you soft reset before killing Anub'arak, the floor will respawn and there will be no way to rebreak it and continue working on Anub'arak.
....
/sigh
Joanadark
Thu Sep 03, 2009 1:23 am

A hotfix has been deployed that will prevent the instance from entering a bugged state where Barrett does not spawn after a soft reset. If you haven't gotten to Anub'arak yet, you'll be fine now.
For those of you already afflicted with this bug in your saved raid, I'm still working on a method to correct the issue via hotfix for everyone so afflicted.
In the meantime, our customer service staff has been informed how they can resolve the bug for a raid with a bugged instance.