I can also though see WWE finding a loophole, saying that whatever he tests positive for (if he does indeed test positive) isn't on the banned substances list of their wellness policy. It would though have to be something that they could pass off as not being on the list though. If it's PED's or something hardcore like hat then of course their hands are a bit more tied.
What strikes me as odd though is that Lesnar didn't have to take that test. Because he was just competing in a one off match for UFC as opposed to being one of their regular fighters he was exempt from taking the test. He only took it to prove a point because he was getting called out constantly for being on something otherwise he couldn't look like he does. Why would he have taken the test if he knew that he'd taken something?