What must be remembered when these pilots left, was that the mining industry was winding down and they feared loss of employment. At the time just having F100 experience would have made it difficult in obtaining another position when competing with other qualified pilots. This resulted in them applying for other positions where they hoped they could obtain endorsements on modern equipment.
It appears they have been quite successful. From what I can gather they have been able to obtain endorsements on the B777,787,767,A330 and A320. and achieve several years of international experience.
Now, to get to your question. I can't give you an exact number but it would not be to difficult to obtain who wishes to come back, after all they have achieved their objectives. I'm sure the company through the pilot group has ways of contacting them. There are some in the Middle East, HK and the Far East. Try Linkedin you will find a few.