No Empire lasts forever. The way this country is going, it might be sooner than later too. I guess it depends on who you are, and how well you like Americans but their could be another way too. A way they could please everyone. That is the day, were we are all evolved enough to know we do not need empires.
Although the United States of America is not specifically mentioned, I will assume that this is the empire mentioned in the question prompt. The US "empire" does not exist, so it has already been replaced by North Korea, China, and several middle eastern countries. Some day, with international trade and growth continuing, another country will outpace the US as a world military leader.
I don't feel that another empire will rise up out of the United States. The country was set up to be adaptable. Because it's set up as a democracy, there are checks and balances, and the people are represented by their local politicians, such as in the Presidential elections through the electoral college. The law can also be changed, though through a lot of effort, if the people want it to be. Because of the way the country is set up, with the people having a voice, it's not easy to see this government being overthrown.
It would only happen if we went into another World War III and our allies turned against us and they combined with our enemies like Korea, Afghanistan and Iraq. This is the only way another Empire would be able to take the place of the American Empire that is here.
I do not believe that another empire will rise to overtake the American empire. I do not think that there is anything true to the idea that the United States of America will no longer be the world's super power. I think that those type of claims are politically bias and without evidence.