I don't see why the WWE should bear even the slightest responsibility for Lance Cade's death. As has been pointed out by others already, the WWE paid for Cade to go through drug rehab on a couple of occassions. So, exactly what else were they supposed to do? If Lance Cade's death is the result of a drug overdose or came about as a result of past drug usage, then it's a tragedy overall but it's a tragedy largely of his own making rather than the WWE.
Everyone knows the WWE has a grueling schedule. It goes with the territory and anyone expecting it to be some sort of cake walk is a fool. To be a wrestler in the WWE, you have to sacrifice a lot. If you want to be a professional wrestler and actually be able to make a living doing it, then you're going to have to sacrifice a lot even if you're working on the indy scene. Constant travel, the wear and tear of matches on your body, accumulating injuries and sacrifice of a LOT of personal time is just how it goes. It was like that with most wrestlers during the territory days and, to a large degree, it's still like that. One reason why WWE wrestlers are able to make such a good living is because of this intense schedule. A lot of WWE wrestlers make more money in a month than most Americans make in a year and they earn every cent of it.
Getting back to Lance Cade, however, he wasn't even an employee of WWE. Cade hadn't been a WWE employee for nearly 2 years. I know that there are a lot of fans that love to bash the WWE for whatever reason whenever they get a chance. That's all well and good if there's actual reason to do so, but this isn't one of them.