Shut down by who? I don't even think they're in the USA. It looks like their main site is in Germany (see bottom of Wikileak site main page). Problem is, if the US Gov takes action against them, they can just move whatever US content servers they have overseas.
Frankly, I'd like to know how they got such materials in the first place. Someone with electronic access to sensitive/classified information is copying it over to unclassified/unsupervised systems. This itself is a violation of US Code 10--10 years in jail/$10,000 fine per violation.
This site is located in Stockholm Sweden. Hmmmm?