Even if there are backup servers which i would not be surprised if there were at least for FFXI. The game is worldwide (unlike other games) all servers share across the world the same information live. If you take down 1 set of servers it would have an impact on the entire play world as an entire audience and some of the load balancing would be affected.

Even if it was possible to split the servers like that I would still be supportive of shutting down the world for a week or 2 if nothing else just out of support of Japan and respect to the players in Japan that would be missing out also as the world changes without them.

However as a company faced with 2 choices below, it is really a no brainer and if nothing else I would just do it out of support. The fact that on XI they will be not charging for April is very nice, although I kind of wish they allowed people to opt in for an April charge and donate and donate all that was collected to the Japanese that need it or services there that need it.
1. Keep and Support a Virtual World so that those not affected can play and risk increased power issues to a ravaged nation, as well as life and death just to keep this Virtual world afloat

2. Turn off the Virtual world, get the cities and towns and power up and running again, then turn it back on taking Real Life and Safety first and Virtual World second. <---- This one is the no brainer