A lot can and will happen between now and 2018. True, Britain will likely be a Euro state, but China's inevitable slowdown over the next decade will likely stall the transition away from the dollar.
the pressure to keep the growth machine going in china has been immense...but nothing grows to the sky, particularly in a global recession. the chinese will learn the hard way, as we are, not to fight economic cycles.
its not an issue of when china will have a major crash, but when and how deep