What to do about a teacher who has checked out?

There's been lots of talk about students who are checking out of remote learning, but we have a slightly different issue: a teacher who appears to have checked out. I'm looking for advice on how to handle this without making matters worse (for both the teacher and the students).

The background is that everything was great in the fall semester. The teacher was teaching, student engagement of course varied. My son was, however, very engaged and worked very hard for this class (which is in a subject that doesn't come easily for him). He went to office hours when he needed help, asked questions in class, and the teacher was responsive, answered questions, explained things, graded homework, and entered grades in a timely manner, etc.

But now with spring semester, everything has totally changed. Apparently, a number of students were caught cheating on the final exam. The teacher was understandably angry and frustrated. But since that time, she seems to have mentally checked out of the class entirely. She doesn't provide strong instruction, doesn't grade work, has entered no grades into the online grade book. My son has reached out for help during office hours, but was blown off. He doesn't know what to do and is, for the first time this year, starting to fall behind. He also has no idea how he is really doing in the class because she has stopped grading assignments. He doesn't want his final grade to be a surprise. 

Normally I try to stay out of these situations and prefer to allow my son to learn to advocate for himself, but he has tried that and, as I said, was blown off my the teacher. But what can I do? I certainly don't want to escalate the situation, but I do think my son has a right to be taught and to be given feedback in the form of corrected assignments. 

Any advice?