Have you read the CC FAQ?A CC license can't be withdrawn. That's the entire point.
Once something has been published under a CC license, licensees may continue using it according to the license terms for the duration of applicable copyright and similar rights. As a licensor, you may stop distributing under the CC license at any time, but anyone who has access to a copy of the material may continue to redistribute it under the CC license terms.
That ostensible power to continue to redistribute it flows, as best I can tell, from the "automatic offer" provision in section 2.a.5.A. I haven't done a comprehensive literature review, but what I've found so far only considers the "automatic offer" element from the perspective of a recipient; I haven't seen anyone consider how an "automatic offer" survives a withdrawal by the upstream licensor of their offer.
None of this is different from the OGL v 1.0a (except that also imposes Product Identity as well as attribution requirements). I mean, some of the minutiae is a bit different, but the fundamentals are not.The only way an individual author/company could be stopped from using this license is if they do not give the proper attribution as per the CC-BY-4.0 contract terms. And that is an easy fix.
No morality clauses, no medium restrictions, nothing.
If WotC stops offering to license the SRD under the CC, and asserts that in virtue of that change of mind no one any longer is the recipient of an "automatic offer", as far as I can see we will be in the same place as when they asserted that henceforth no one would be able to exercise the rights and powers they enjoy under the OGL v 1.0/1.0a.
If you know of literature or cases that have considered what happens to the "automatic offer" provision when the upstream offer is withdrawn, I'd be interested to read them!