from the reddit thread
"So, they unfortunately can de-authorize the old OGL. OGL 1.0a is perpetual, worldwide, royalty-free, non-exclusive license, but it is not irrevocable. De-authorization and revocation function effectively the same here.
Because the old OGL states that you may continue to use any authorized version, and is fully revocable, having OGL 1.1 de-authorize OGL 1.0a is an effective revocation/de-authorization of 1.0a.
However, even though it's permissible under contract law, it does not mean it's an equitable result. This could lead to a lawsuit from relying on 1.0a for so long, only to have it be quickly switched Indiana Jones style.
As a general disclaimer, while I am a lawyer in the gaming/tabletop industry, this comment is not legal advice - it's for informational purposes only, and does not create an attorney-client relationship."