None of the official campaigns in 5e have dealt with the wall as far as I know, and people's individual campaigns don't really get in the way of what is and isn't official. Your world space is always how your GM makes it, and if they want the wall, then they have it, regardless of what the official material says about it. Most of the erratas are mechanical tweaks, not lore changes, and I imagine they did the errata documents to avoid having to do re-prints every few years, which was a thing in previous editions.
In my version of the Forgotten Realms Myrkul is dead and never came back after dying and having his lingering soul devoured on the plane of Limbo by the very avatar of the wall he unleashed into the world. The wall was subsequently altered over time by Kelemvor, who never liked the wall anyway, and (correctly) considered it a tool of fear created by a malicious god who wanted mortals to suffer. This has no effect on the official material at all, and it's up to me to thread my own changes into any future campaigns I run.
