Could you clarify this point?
Here is the text of section 13 of the OGL v 1.0a:
Termination: This License will terminate automatically if You fail to comply with all terms herein and fail to cure such breach within 30 days of becoming aware of the breach. All sublicenses shall survive the termination of this License.
This is the only provision in the OGL that deals expressly with the issue of termination. But it does not say that it is the sole basis for termination/revocation. The letter sent on behalf of Sad Fishe says that
Section 13 sets forth the sole condition of termination of the license . . . Outside of what is given, Wizards has no authority to terminate the license, both with respect to prior published content and future published content under the license.
That claim rests on the premise that the specification of one mode of termination, and the failure to specify any others. confines the power of termination to that which has been specified. This is what I mean by identifying an implication based on construction/interpretation of the instrument as a whole.
The Sad Fishe claim also leans heavily on the statement about survival of sublicenses. (At least, that seems to me to be the basis for the claim about future published content.)
As I said, I don't think these claims are hopeless, but nor do I think they are certain. bmcdaniel, who clearly is more of an expert than me, says the status of sub-licensees following WotC's revocation of its standing offer is not clear. I'm not going to contradict that!