There's two statements that I use in my business. "Never Beg a Person to Join your Business." & "Never Beg a Person to stay in your Business."
If you were a good sponsor, you would have given this person all of the information they needed to become successful.
There's too many fish in the Stream, to worry about the one that got away. Maybe in the future that person will come back more determined to become successful with SFI.