If you believe either sentence you clearly know nothing about economics.
Even in the position we're in today, we're still the strongest economy on the planet. We still have the largest influence in the financial market. Our GDP is still about three times the next in the list. Hell, it's fifteen times your country's. Our PPP is still the highest and the only time in recent history we've dipped below any other country in the global competitiveness report was to the Swiss in 2009. For a month. Hell, California alone is still in the top ten of GDPs and its completely bankrupt.
The dollar is still today the most important piece of currency the world has known since and including the Roman Empire. More business is done with the dollar than all other currencies put together. We are still the leader in international trade. We import more before breakfast than most other countries do all month. And still, even in the midst of a global economic crises, we still have the ability to release a new iphone and have millions of people with expendable income blow more money on crap they don't need.
Even at our worst we're still on top. Even at our weakest we're still stronger than everyone else. The entirety of the European Union - which was only able to spend so much money on its social services because it depended on American military strength for protection - is the only thing that can come close and they're still a haphazard collection of people too stupid to learn how to play well with each other and are still going bankrupt.
Face it; we go, we take every trading partner with us. With all those trading partners in the hole there will be nothing to prop up everyone else. You think Australia is entirely self-sufficient? Have fun with that.