This happened to me with some slight variations in that my PI basically lost her mind, flipped out, turned on all of the students, and ended up terminated. She left the state and put me, the new grad student, in front of her classes for weeks.

I'm going to be honest with you. I don't feel like I ever fully recovered. She did some things to intentionally harm me and tried to lay blame for her missed deadlines and disappearance. She tried to have me kicked out of the program with a lie.

I had full support of the department as they had multiple reports of her misbehavior from other students/faculty. However, I felt betrayed by them because why did they keep letting her take students if they knew she was unstable?

Where my story is most relevant to your post is that I did end up going outside of our department for research. There was another researcher in a completely different field rocking similar interests. It was a great experience but a little lonely, in the end.

I remember how anxious I was for the entire year this drama was unfolding in my program. It really scarred me pretty deeply and so, I wanted to post and encourage you to take care of yourself first in all of this stuff. Trust your gut and protect your career.

Epilogue: After the PI left, the program director became my new advisor. She had her original students and I felt like an afterthought in our meetings... especially since I was researching outside of our department. It was rough.

Additionally, she ended up being forced out of the university one year after I left because of continuing fall-out from my original PI/advisor. Two dozen students had filed complaints and others had pulled out of attending when the drama came to light.

I kept my mouth shut through it all and only ended up in that field for a handful of years. I went back to school in another field and was very anxious throughout the application/interview process. I still don't have a good handle on how to explain it.

I feel like I did all of the work but don't have the same bonds as my peers. The networking part blew up in my face. Both of my advisors left the school amid controversy and my PI is a totally different discipline that can't help me beyond general references.

I hope you have someone to guide you through this situation. Best of luck to both you and your PI. Witnessing hell in academia has the potential to leave deep scars... I know, from experience, and I hope that doesn't happen to you.