I was invited to resign and left China without getting a release letter.

Does this mean I can never work in China ever again?

First, no! China will never stop you from leaving, and you are more then welcome to cancel your resident Permit at the PSB and thus get a 30 day L visa, BUT BUT BUT, can I hear one more BUT please, (ok Thanks) But your company will still own the rights to your passport for future jobs, meaning that you will neverbe allowed to get another Resident Permit again unless you go back to your Company 1 day or 50 years later and get your "Release Letter, no new company can hire you until you get that letter of release, it'll be in the computer, so don't fool yourself into thinking that "Hey I can just get another resident permit.""..

i heard a story, heard being the key word here, of a friend of a friend living and working in china. his school was very shady and liked to hold the foreigners accountable for everything that went wrong. so this person decided to quit and leave the school. the school burned his apartment, and told the local police that the foreigner did this out of spite. the local police banned him from traveling on trains and planes until he paid the school an absurd amount of money.

now with that story out of the way, i don't think it is very likely that the school, or government will do so much work to keep you from leaving china. their new policy seems to be kicking foreigners out of the country, not preventing them from leaving. but still, try your best to leave on good terms... and don't light things on fire...

It depends on the reasons, why you were 'invited' to resign.

Dial SAFEA in city you worked, and ask them either for Release letter or if you'll be still able to get Working permit.

Enter 'SAFEA' in search above for address and contact nos. in your last working city.

You can also apply for new position in China. Your new school will tell you, if SAFEA approved Working permit and Invitation letter for new Z visa.