Seeing as accepting the license and using open content licensed under that license requires that you copy that license, you actually can't lose copyright as long as the agreement is in place.If you agree to license your copyrighted work to me under the terms of the OGL, we have an agreement. WotC is not a party to our agreement.
But WotC have two roles in our agreement that I can see. First, they own the copyright in the text of the OGL itself. So if we reproduce that text in our agreement, and require others to do so when they enter into licences with us, we may be infringing WotC's copyright. I don't know if there is a fair use argument here, as I'm not a US copyright lawyer. There may also be an argument from reliance or estoppel or waiver or implied permission, based on (eg) the statements on the OGF website that you refer to.
That is, the requirement to copy the text implicitly grants copyright (I don't own it but I have the right to copy it) because I am required to do so by the terms of the license.
... or so it seems to me. I think 'copyright' is not grounds for not using the license.
If the license is revoked, so is the need to copy it, which could mean I no longer have permission to do so.
"You may use any authorized version of this License to copy, modify and distribute any Open Game Content originally distributed under any version of this License" means it's up at the discretion of the licensee, not the contributor. I can't force a licensee to use any particular version of the license, they can choose which one they want.The other role that WotC has is that, under section 9 of the OGL, we would have agreed with each other to allow our licensed material to be re-licensed under other versions of the OGL authorised by WotC.
I suppose it could happen that an updated version could put additional onus on the contributor and thus be of interest to the licensee -- "contributor must pay licensee for each use" sort of clause, but it seems greatly unlikely the author of an OGL update would want a clause like that in it...