Hard to say, action figures/doll have been around since the times of the Greek Gods. I think the concept of the action figure/doll will be around forever, G.I.*JOE specifically? Maybe a ten or so years, but if it can stay realevent, maybe longer. Look at Star Wars, after ROTJ, those figures sorta died down, then had a resurrgence in the early 90s, then the SEs of the movies came out and sparked people's interest again, then the prequels and now Clone Wars. If we're lucky enough to get a good cartoon again out of G.I.*JOE, they may be around for a while.
Video games may have a huge market, but for forty dollars, a parent can buy a vehicle and a couple figures for their kid. Most kids I know lose interest in video games before they lose interest in their other toys like figures/dolls and toy cars, that sort of thing. Video games aren't going away, but I don't think they'll completely erase action figures.

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The United States will conquer Terrorism with the help of God and a few Marines.

Some people, when trying to avoid thinking about those things that cause them pain, turn to drink, or perhaps food, or drugs... I turn not to any of those... I collect action figures, turning my mind to the hunt, so that I might find a mote of peace... Over the years, I've found that alcoholism is much more socially acceptable by far.