According to the FAQ, yes. But not according to the text itself. Arguably, it's a gross simplification of the following interpretation (emphases mine in the following).
From section 3: "Offer and Acceptance: By
Using the Open Game Content You indicate Your acceptance of the terms of this License."
"Using" is defined as to "use,
Distribute, copy, edit, format, modify, translate and otherwise create Derivative Material of Open Game Content."
"Distribute" is defined as "to reproduce,
license, rent, lease, sell, broadcast, publicly display, transmit or otherwise distribute".
Indeed, having "Used" OGC like this by
licensing it, WotC "
must affix such a notice to any Open Game Content that [they] Use". If they don't, they're in breach. But sublicenses survive terminations for breach. So there's no "putting the genie back in the bottle" if it's already out there.
There is then a case that WotC, having
licensed OGC according to the license, has
accepted the terms and is thus contractually bound to continue doing so. Like Bob Tarantino writes, "open content must remain open for all future users."
@pemerton might disagree, but I hope he'll tell us why! I suspect this somewhat circular reasoning is unappealing for some reason.