Quitting your job while on expat assignment (Johannesburg)

Hi there,
Has anyone quit her job while on an international assignment? Is anyone planning to do so?
I'd like to share ideas and experiences on the subject.
Lets put it this way... a dear friend of mine :) has received a very good job offer but the new company is asking him to start as soon as possible. This means he must resign from his job just a couple of months before completing an important assigment abroad (which he suggested in the first place).
He's having some financial concerns because his assignment had a "re-pay all expenses incurred" clause should he have resigned, and he's not totally sure about the exact figure.
Has anyone had to deal with a similar stuation before?
Cheers,
Davide