What I find mind boggling about this is that there are definitely parties interested in maintaining the integrity of this license, including the public.
To illustrate: For the sake of argument assume wizards go defunct in a way that make their IP effectively unenforced (as
@pemerton points out, going out of business might not be a sure way of this, but there might be other ways). Moreover assume Paizo is thriving.
Now assume a new company A publishes a work using 5.1SRD under OGL 1.0a, but include the claim that it is "compatible with D&D". From what has been said, Paizo is then free to inform A that they are in breach of OGL 1.0a. However what if then A is making a claim (highly unlikely to hold up in court) that they indeed is not in breach?