"What steps will government then take to bring retirement money and spending back home? "
The very "steps" that are embedded as part and parcel in the bill ... making the U.S. the world's largest tax haven.
If embittered individuals choose to leave the US, they're certainly free to do so - but that's been going on for a long time now due to the income tax. More will undoubtedly be returning with their capital once they see the FairTax has passed. They'd be foolish from an economic standpoint not to.
A tax haven for investments, not a place to live and consume.