> Don’t think his claims would stand up at all of lawyers were involved.
Absolutely 100% would stand up. If the US and UK have one thing it's strong copyright protections that favor the copyright holder. You can't accidentally transfer owner of your copyright with an off-handed remark and this is well established. If I commission an artist for a work the artist retains the copyright unless it's explicitly transferred to me or if the artists is my employee -- contractor isn't enough.
> his poem could be removed
That wouldn't stop it in general. It comes down to the specific license terms. Copyright deals with performances and his work has already been performed millions of times. That can't be undone. Pirating a movie, watching it, and then deleting your copy doesn't make it not copyright infringement. If the contract said only for use in Minecraft then any merchandise or Minecraft: Bedrock. Worse, licenses aren't by default transferable. If I give your band a license to play a song I wrote and you leave to join another band it doesn't follow you unless it was explicitly stated in the contract. So if Microsoft did something with the licensed work that wasn't under its legal subsidiary Mojang that might also be a problem.
I'm not saying any of this happened but hopefully it's enough to demonstrate that "obviously a judge would rule that a reasonable person would have assumed the work came with copyright assignment" is very unlikely doubly because the fact that they asked him for assignment later means they knew.
Absolutely 100% would stand up. If the US and UK have one thing it's strong copyright protections that favor the copyright holder. You can't accidentally transfer owner of your copyright with an off-handed remark and this is well established. If I commission an artist for a work the artist retains the copyright unless it's explicitly transferred to me or if the artists is my employee -- contractor isn't enough.
> his poem could be removed
That wouldn't stop it in general. It comes down to the specific license terms. Copyright deals with performances and his work has already been performed millions of times. That can't be undone. Pirating a movie, watching it, and then deleting your copy doesn't make it not copyright infringement. If the contract said only for use in Minecraft then any merchandise or Minecraft: Bedrock. Worse, licenses aren't by default transferable. If I give your band a license to play a song I wrote and you leave to join another band it doesn't follow you unless it was explicitly stated in the contract. So if Microsoft did something with the licensed work that wasn't under its legal subsidiary Mojang that might also be a problem.
I'm not saying any of this happened but hopefully it's enough to demonstrate that "obviously a judge would rule that a reasonable person would have assumed the work came with copyright assignment" is very unlikely doubly because the fact that they asked him for assignment later means they knew.