Would that hold true in all aspects of a potential breach of the terms of the OGL? For instance, if they were to properly declare what part of their work was Open Game Content, but didn't list a copyright notice for their own work in the Section 15 of the OGL, that's technically a failure to follow the terms of the license. So in that case, if they failed to correct that in thirty days, the license wouldn't terminate for them?
What licence? In the scenario you describe, there is no licence, only an offer.
Again, the offer may fail for want of certainty, in so far as it tells prospective licensees to replicate a section 15 statement that doesn't exist. Alternatively, it may be that the absence of a section 15 statement by the licensor means that their licensees can trivially comply with their section 6 obligation.
So if I'm understanding you correctly, using WotC's license isn't enough to enter into a contractual relationship with WotC? And as such, WotC has no standing to claim breach of contract if it doesn't involve their content.
More or less. You use the phrase "WotC's licence". But this is ambiguous, and you're not really disambiguating it.
Let's suppose that I purchase a car, that was built by Toyota. In one way of speaking the car is Toyota's - they designed it, built and probably own intellectual property rights in respect of various features and/or components of it. In another way of speaking the car is mine - I own it as a piece of personal, tangible property (in Australian law we call it a chattel or a chose in possession - I suspect the same terminology is used in US law).
Talking about WotC's licence can refer to
a piece of text in which they own the copyright. It can also refer to
a licence agreement to which they are a party. If enter into a licensing contract with you using (i), that does not make WotC a party to my contract with you. I mean, you could set up a webforum and copy your terms of service from the ones that ENworld uses. You could even call your forum "ENworld". Morrus might have claims against you for copyright and/or trademark infringement. But he would not have any power to change the legal relationship between you and your forum members.
while the license does hold that termination occurs automatically within thirty days if a breach is found to have happened, there seems to be an expectation (perhaps mistakenly) that the party whose content was used in an OGL product where the breach occurred needs to take some sort of action in this manner.
Who holds that expectation?
If that's not the case, then I suppose the question is, doesn't that mean that the breaching party has already lost their right to use the OGL (once the thirty days has passed with no correction having taken place), as the license has terminated for them? In which case, WotC (based on the MM2 example posted above) has lost their right to post material under the OGL?
You are still treating the OGL as a statute, rather than a written set of terms that two parties can adopt for the purposes of entering in a contract with one another.
If WotC's licence from WW terminated for breach, then that might expose it to a lawsuit from WW (eg for copyright infringement; perhaps also for breach of contract). That would not affect WotC's power to enter into new contracts with WW, nor its power to enter into contracts with anyone else; nor the terms of any of those contracts.