I haven't the first clue of what they are going to do with their future. It is my sincere hope that they start a business or two of their own and become wealthy enough to employ several other people.
What does that have to do with working in the here and now?
It's relevant because they are a statistical anomaly. You have no right to "get lucky."
They can't, or won't work like that forever, so you are going to have to replace them, eventually.
When you can't replace them for what you were paying them what are you going to do, look for more "foreigners?"