That is a question that has no finite answer.  The best I can suggest is to weigh the pros and the cons of living here.  Then, with do the same for whatever country you want to go to (or back to as the case may be).

If more days than not are a drag on you mentally and physically in China, then it is probably time to pack up and leave.  We all have our thresholds of what we can tolerate.  I have seen it range from 3 days to 30 years for different expats.

Life is not a picnic anywhere in the world, but that doesn't mean we should stay someplace and torture ourselves.

When I felt like giving it all up and getting on a plane, I would wait a couple of days before I bought the ticket.  Normally, after that couple of days, I wouldn't want to go any longer.  That method worked 6 years for me.

For me, life is about responsibility. If I didn't have a wife and child i'd be travelling all over the world right now. If you have responsibilities, then you have to man up (or woman up, depending who you are) and get on with it. But otherwise, you shouldn't be asking this question, you should be following your heart. If you're done with China, hit Brazil. Go to Kenya. There are so many places to visit. You shouldn't even be asking this questing.

Personally speaking, it was when I realized that I was fed up to see Chinese people all around me, every day, everywhere I go and that I couldn't stand to see them any more, neither their rude behavior, their selfishness and arrogance.

Then with my wife being Chinese, it was a kind of perpetual Chinese harassment in my life. And we always had arguments.

We move back to my country, life is much more difficult than in China, but at least, I feel now that my wife is part of this exotism that I often see in my country. Almost no arguments, great time to laugh and travel around. We spend a great time with our child to do many things that he could hardly do in China because of the costs (swimming, ice-skating, feeding farm animals).

When you feel like that you may kill each Chinese you see, when you feel that you cannot hear anymore the 5000 years of history and the greatness of Chinese people, etc. When you brain starts to scream and give you weird ideas, then it's time to leave.

When you're in a hospital and someone has 2 clucking live chickens in a basket underneath their bed in the maternity ward, with their baby in the cot beside them.

When you seriously realize there is no professional advantage to be there. 

Differnt for everyone  but if you are fed up with China right now then it may be time to go....unless you think things will get better.  Also got to think about where you would go live, would you go back home or to another country and would you enjoy it there or would you end up going throw China withdrawls and miss it.

It's really hard to answer this question cause everyone is different.

For me, I'd like to leave China right now to be honest. I enjoy it here and have had a great experience but I'm pretty home sick and sick of everything around me being Chinese.  Only reason I'm out here is I'm waiting for a GF to finish school first then I'll marry and move back home..... although after seeing a wedding recently in China and all the stress that comes with it, now I'm scared to get married hahah

When you begin to get up every morning and just don't want to go through the hassle of leaving your apartment for a stinking bus, a day of being lied to by colleagues and an evening of getting hideously drunk to forget the rest (actually, that was the part I enjoyed).

When every action you see Chinese people do elicits a cry of, 'That's f**king stupid!'. Or when you feel there's no point trying to make friends as you can never get an answer to a question worth hearing.

When you sing songs at the top of your voice decrying the illegal occupation of Uyghur lands by the PRC, knowing full well that the words 'East Turkestan,' if heard by the police, can get you jailed.

When the thought of another night at the local KTV makes you want to scrape your brain out with a chopstick through the nose. Not because karaoke is so hideous in and of itself, but because if that mic gets pushed in your face one more time you're going to cause violence to that person.

When you haven't taken a solid shit for six months ...

I can't stay out of Canada for more than 182 days or I loose my health coverage. After183 days I have to stay in the country one year before it kicks in again. All this time I'm paying income tax , sales tax, property tax whether I'm in country or not. So before 182 days I pick my return flight. Thanks Canada that makes sense !

 When Its time to go I don't want to leave. On my first trip I stayed up all night rather than waste my last time in China. I didn't want to go home last time, but in between I was pissed off enough that I started to pack and search for a flight. I couldn't find anything under $3000, so I stayed.

I think Guys and Gals, It is right time to leave for me. I have all of the symptoms stated above here. For sure, I am making this decision for long time, biggest trouble was, and still is, my wife, her ties to her family. But all is going better, after many arguing, when last time i really screamed out most of my feel about staying here. I refused really to stay here more than additional 1 year. Doing my preparation, i really wish let all is that easy like just buy tickets, package some clothes and bye bye China. 

  I've like China before, the first years. But the more i stay, the more i hate all around. Even i can not stand new constructions, i don't see it as well doing of the companies. All i see is shit and crap  Can not help myself, no way to pay extra charge in kindergarden, because our son is not yellow enough. No way go to hospital again and again without any help after waste whole days just in waiting lines and pay for everything before you get any answer from "specialist". No way eat rice everyday, And more and more and more of this. Btw, i already forgot, what is solid shit  just can see my son have very hard shit, after drinking this milk stuffed with who knows. Can't wait that day when i'll do my check-in on Pudong airport

Probably when your elbow has slipped off the bar a few times in the last hour,

your bank card is in your apartment, and you only have enough dosh left for the taxi home.

No big deal you can start again the next evening.