Can a closed economy flourish? I was wondering if it is possible to run a country based only on domestic economy and not to enter the world economy. Basically, if certain economy of a certain country fails and poses threat to world economy, can other countries seal off their economies and still function with sustained growth and flourishing markets based on domestic economy itself?

I know this a naive question, but I tried to find an answer on on the internet and didn't get a satisfactory answer.
It depends on what you mean by "sustained growth" and "flourishing markets". 

Clearly the Earth as a whole is a big market. If you do not look at human made borders: the global economy is currently growing and some would say it is flourishing. There is no physical reason why this could not be done without the borders.

There are areas where the current technology cannot support the current population without outside help. An example is the heavily industrialized North Korea (which seems to motivate your question) which gets large amount of aid in food from the UN.