Unless they've changed the policy, if you leave, your visa/res permit will be cancelled, so you can't come back without new visa. Right now China is issuing VERY few visas. Normalcy should start to return when a few more countries get their daily new cases crushed down to near zero or when an effective vaccine comes out. For example, I think it's within the range of possibility for visas go back to normal for people in New Zealand sometime in the not-too-distant future.
If you do leave now and manage to get a visa to come back, expect a quarantine.
For those teaching in China now, take advantage of the reduced competition - look for the best job you can qualify for before the fall term starts. An effective vaccine may be out within a few months, or may take over a year - there's NO way to be sure at this point.