Not exactly, there are chips made by other American companies, and lately chips are being made in other nations
Now these are not currently competing in the desktop arena with Intel, but if AMD were to disappear, I am sure someone would see an opportunity and step in.
Also, the US antitrust law wouldn't apply if AMD went under, there would still be competition in the server market,... and as long as Intel didn't price gouge the desktop market (which if they did, I could see a company with resources and ties to current technology stepping in and filling the void)
Competition law, known in the United States as antitrust law, has three main elements:
prohibiting agreements or practices that restrict free trading and competition between business entities. This includes in particular the repression of cartels.
banning abusive behaviour by a firm dominating a market, or anti-competitive practices that tend to lead to such a dominant position. Practices controlled in this way may include predatory pricing, tying, price gouging, refusal to deal, and many others.
supervising the mergers and acquisitions of large corporations, including some joint ventures. Transactions that are considered to threaten the competitive process can be prohibited altogether, or approved subject to "remedies" such as an obligation to divest part of the merged business or to offer licences or access to facilities to enable other businesses to continue competing.
Source:
http://en.wikipedia.org/wiki/Antitrust