Depends on what you mean by fail, I suppose. I'm of the opinion that Obamacare has two goals, the short term goal of providing access (via both subsidies and forcibly redrawing the risk-premium equation) and the long term goal of destroying the private insurance industry and moving everyone to a single payer government system. I don't see it outright failing, although obviously there will be winners and losers. Some people will be able to afford health insurance who previously could not, some people will find their health insurance suddenly much more expensive (though still within rough equivalency as to percentage of income.) Some who had crap insurance or no insurance through employers will find they now have better insurance, some will find they no longer have jobs. That's unavoidable; can't have major change without winners and losers.
It will no doubt run woefully over cost projections and have a lot of collateral damage, but that's only failure if you discount the long term goal. And it won't meet it's target goals in percentage insured - such programs always fail in that limited sense because they must assume a static model whereas in the real world behavior changes with risk and reward and punishment - but those failings will be addressed via administrative changes. Either way, most parts of it will have a constituency, people who value that particular part whether or not they support the entire bill. Thus I don't see it ever actually failing. Even federal programs that are miserable failures in meeting their nominal goals, such as the Department of Education or the Department of Energy or the War of Drugs, never really fail, they simply shift the goal posts. The Department of Education has been a miserable failure at improving educational results, so it does standardized tests so that even if education keeps getting worse, at least we can quantify the problem, and it identifies problem school districts and attempts to deal with them directly with funding or control. The Department of Energy has been a miserable failure at getting us off imported oil, but funds important research and manufacturing initiatives aimed at clean, renewable energy and energy efficiency. Like any entity, government programs must adapt or die, and I see no reason the ACA won't likewise adapt and find things people want done in place of things it cannot do. In fact, as much as I viscerally dislike the idea of moving health care to the federal government and especially to an un-elected bureaucracy, in some respects this will make it much easier to adapt. Consider the ADA - virtually every attempt to fix its problems utterly fails because so many powerful entities have wish lists and vested interests they wish addressed, so the bills typically get so bloated and controversial that even their sponsors won't have them. The ACA will have decisions made for political and/or ideological reasons, but it will also be much, much more easily amended to react to changing reality.
The long term goal is even harder to visualize failing. We've become a nation that expects high quality health care at someone else's expense - which is really just part of our overall entitlement mentality. We've also become a nation that increasingly shuns personal responsibility; when we have young people who do not believe Social Security will be there for them but also don't want the responsibility of managing their own retirement account, obviously individual health insurance is on its way out. (Although ironically I could just as easily make an argument FOR the ACA on this same basis, for breaking the employer-controlled health insurance equation and returning control to the individual.) This movement is probably irreversible, so there is little likelihood that the ACA will fail in this goal either, although obviously the exact form of socialized medicine has yet to be determined.