Two years ago I was working in China on a Z visa but only completed half of my contract before returning home.
I am wondering if I will be able to obtain a visa or if I will be refused/blacklisted.
You should be fine. Apply for jobs and find out.
If you have a new passport since then even better.
But be honest on your application form.
You can call SAFEA, and ask them about it.
In order to get new Working permit at SAFEA (Foreign Expert Bureau), you must have Release letter from your last employer.
If you complete the Contract, employer must give you Release letter in 30-days after your last working day.
It's difficult to say about 'not completing the Contract'. I guess, SAFEA probably won't grant new WP to a FT with violations.
You have two options:
1. Call SAFEA, and ask about it;
2. Apply at new School in China. When School will start with WP application, SAFEA will tell them if you're in violation, and it will deny issuing new WP.