In terms of current rankings, global finance is basically the old British Empire plus Zurich and Tokyo. Having English as the lingua franca is a plus, because bankers, lawyers and operations staff can flit around the globe relatively painlessly.
A logical long-term successor would be Frankfurt, currently placed at 18 on the global list. But would French, Italian and other European leaders - excuse me, "leaders" - be comfortable with Germany as the financial as well as commercial superpower of Europe?
That said, England will remain a major world economy with a very long history as a financial center with widely understood rules. It's decline would probably take decades.