The Zambonians will either keep the loot in Zambonia, thus lowering our money supply and increasing the value of the dollars that you and I have, or the Zambonians will send it back to the US where it will still fuel our economy.
ECON-101
If the billionaire creates jobs in another country, the people in that country won't be sending money back to the US. They will be sending product back to the US, which will be paid for in US dollars - dollars that will be sent offshore to pay those foreign producers for their work. The effect is a net out-flow of wealth. If you think that our trade deficit is bad today, just wait until there is no money to fund business expansions and retooling in the US. With a glut of dollars flowing offshore, the value of the dollar will take a nose-dive.
The only hope of preventing that is to keep the wealthy here. The people in Congress know that. That is why they are so busy passing laws trying to force the wealthy to stay or punish them for leaving. The problem is that in their lust for power, they have chosen to use a whip rather than a carrot and history has shown us repeatedly, that only reward, not force, can keep wealth from leaving any country.
(BTW, isn't Zambonia where they make the famous Zamboni Ice Rink Machine?)
As you suggest, the "Brain Drain" is a problem. But, since you only have to make about $120,000 per year to be in the top 5% of income earners and most PhD's (other than teachers) and other high level researchers and engineers make well into the 6 figure range, we are probably talking about many of the same people. Furthermore, since over 36% of our taxes are paid by the top earning 1%, if only that top 1% (roughly 1.2 million) should leave, it would mean that those who remain would face a greater than 55% tax increase, just to stay even.
At the current expatriation rate of about 100,000 per year, that could easily happen in 12 years. But, since the expatriation rate has been growing in recent years, the laws that are driving expatriation are getting more sinister and the media is beginning to take notice, the expatriation rate will probably continue to increase and the top 1% could easily be gone in as few as 5 years. Regardless of how fast it happens, as the people who pay the lion's share of the taxes leave, that enormous tax burden will fall upon the poor and middle class.
When taxes go up, productivity goes down, which results in lost jobs, which in turn, results in more people on welfare, which forces taxes even higher, which results in lower productivity, which results in lost jobs, ...
Of course, if you are a Marxist, you believe that all jobs emanate from government and that only those in government should be allowed to have lot's of money. In that case, you aren't alone. There are about 534 people in Congress who agree with you. But then, that's why things are going south so fast.