According to Splinterverse (in this post
) the authors are commission art to repalce the illegal art so they can release it on DM's guild. I kinda think that proves my point.
Of note, if they do release it on DMsGuild, they will need to remove it from whatever site they have it posted for free (per DM's Guild requirements).
PS The Elmore art "Dragon Slayers" is in the book, fairly early. I am not sure who has the copyright on it, but normally it would be TSR/WotC. That is also not the only, non original, art.
I just looked again and there is other suspect art, but it is honestly not as much as I thought. I imagine they can get this cleaned up for the guild without much effort.