They may decide to leave before their bond is up.
Many countries laws do not accept such bonds, especially if paying for their own type rating BEFORE being employed was a requirement. The court would ask for a detailed breakdown of the bond costings.
Obviously you wouldnt go to court in Vietnam, you may lose there, but VNA would have to take you to court in your own country and would probably realise they would be waisting time and money on a case they would likely lose..