The U.K. existing the EU will be a big blow to the worlds economy especially in the developing nations. Britain's financial contribution to EU is so much that its exit will greatly affect the projects carried out or funded by EU. Another thing is the trading regulations that will have to be changed since it will no longer be part of the EU not forgetting the ripple effect on the Euro.
There is no doubt that Britain's exit from the EU would wreak economic devastation in Europe. However, that's what happens every time a country wants to be independent. Think about the American Revolution. When the United States gained independence from the British Empire, it causes economic chaos around the world, but that doesn't mean that the United States shouldn't have declared independence.
No, Britain's choice to end their involvement with the EU would not bring economic chaos around the world. The worst effect of the decision would impact Britain. They would have to change their monetary system but their government will remain intact. There could be a slight ripple felt in the economic markets, but the markets would recover in a short amount of time. Any upheaval and chaos would be centralized to Britain and her citizens, as well as those bordering countries while she regains her singular voice. Britain is not so deeply vested in other countries that it would topple them, unless the country is already unstable. The fact that Britain is seeking independence could actually strengthen economic markets with new growth and opportunities around the world.
British economy isn't what it used to be. Back in the 15th, 16th and part of the 17th century the entire economy of the civilized world revolved around the doings of the British empire. For better of for worse, that has changed and now it's the United States and China calling the shots economically speaking around the world. So no, the UK leaving the EU would hardly be noticed in other parts of the globe.