Why quit and let them have their cake and eat it too?
You can go on sick leave, get paid and stay at home looking for another job. Then, after six months of this and HR threatens, you can return and "eat it" or quit.
But quiting right away is exactly what they are looking for: getting rid of expats at zero cost. And don't be surprised that if and when you quit they cancel your return ticket home "because you have not honored your comtract" and then have to pay for your own. Don't believe it? Try it! If they pull sh*t like that, who are you gonna complain to? Amnesty International? ha ha ha