I see people saying that "perpetual" is ambiguous or depends on the context. This is not the case in American licensing law; "perpetual" has a very specific, standard, boilerplate meaning, and irrevocable is absolutely distinct.
Here is an example: an agreement between GlassHouse and Dell (link below) states that GlassHouse grants Dell "a
perpetual,
irrevocable, royalty-free, fully-paid, nonexclusive, worldwide license..."
That should seem familiar, because a similar provision is in the OGL. This list of adjectives is standard license boilerplate. Notice, however, in the OGL, the word "irrevocable" is conspicuously absent from the standard list of adjectives. That absence in an otherwise standard boilerplate provision is extremely important in the eyes of an interpreting court. If the OGL was intended to be irrevocable, it would say "irrevocable." In most courts, that argument will beat any other argument about reliance, or promissory estoppel, or breach of contract claims (revoking a license is not the same as breaching a contract), or anything else.
The agreement between GlassHouse and Dell also states: "
Irrevocable Grant. In no event will the rights granted in this SECTION 2 be subject to termination, revocation or any further limitation, in whole or in part, for any reason, and all such rights shall remain perpetual, unlimited, and irrevocable under all circumstances."
Intellectual Property License Agreement
Now THAT is an irrevocable license! THAT should have been in the OGL if the original writers had really wanted to take away WotC's ability to revoke the OGL.
Here I will rest my case.