In the conclusion of their article "The Political Economy of Imperialism, Decolonization and Development" (British Journal of Political Science, July 2011), E. Gartzke and D. Rohner refer to "American enforcement of a norm of territorial integrity,...[which] could decay if the United States weakens or developing states become more capable of conquest."
I don't think this statement, especially the first part of it, is very convincing. The territorial integrity norm is quite deeply internalized by most states, making its enforcement largely unnecessary. In other words, its effectiveness is not generally dependent on enforcement by a powerful state. That situation conceivably could change but there are few indications that it's going to change any time soon.
From linkage at DofM I see that Richard Price (who wrote a book on the chemical weapons taboo) is making a rather similar point about the norm against chemical weapons use: it will continue to be generally observed, even if the U.S. does not enforce it by taking military action against Assad. (I haven't read Price's piece yet, however.) It might be interesting to compare the number of times these two different norms (territorial integrity and chemical weapons) have been violated in recent decades, by whom, and with what consequences.
[Note: post edited slightly after initial posting]