Anyone who thinks Activision or Bethesda is falling anytime soon is out of their minds.
EA probably shouldn't be in question, either, except that they're very much at the mercy of licensed content, so a massively hypothetically fall is technically possible if everything goes wrong at once.
Either way, I don't think it would be a big deal to lose either Activision or EA. In terms of self-developed content, both could be replaced. FIFA, the NFL, another big budget military shooter--those games would get made by someone. That's way too enticing a vacuum for the market to ignore. In terms of publishing, I don't see much of a problem, either. Other publishers are already growing and more would step up if given the opportunity.
Bethesda would be the biggest loss, assuming their IP don't get snapped up. The IP they own aren't easily replaceable and would possibly even hurt the video-game market if they disappear.
From a personal standpoint, EA and Activision could disappear tomorrow and I'd lament very few of their franchises biting the dust while hoping the most talented teams reform elsewhere (BioWare comes to mind). Bethesda vanishing, though, would devastate me. I know nothing about it but the next Elder Scrolls game is automatically my "most anticipated" ... until the next mainline Fallout comes around.
