PRC just need to fly out of Singapore. And the Singapore gov. cannot do anything because is not a big crime like killing/murder. Interpol cannot do anything also.
They only Singapore gov. can do is sue/jail them and hold theirs passport once they come back. Those come back is idiots once they run away.
That the risk gov. have to take when they give scholarship to others country. That why once they graduate gov. will provide them a job or before graduate already been offer a job so they will not fly away to reduce the risk of breaking Bond.
Running away is the right thing to do. It is very LKY.