You guys should reffer to the timeline of events in the pdf files. FFXIV will go down for quite a few month and once they shut it down the first time it will not be turned on again.

Why? Because 2.0 is played on new servers and even though we will be in a completely new world, our characters will retain all the progress we've made so far.

This translates to the following: if they transfer character data once, but then turn 1.0 back on and we update that data with new adventures and items then the data transfer process will need to repeated yet again, simple as that, SE will not do more than one data transfer.

It's safe to assume that once 1.0 goes offline, it will be for good.