Who got to keep an ovary?

I'm getting a hysterectomy and cystoscopy next week. Right now, the plan is to take everything except for my left ovary ("unless it doesn't looked good").

My question is, if you were left with one ovary, did you need HRT?

My surgeon is saying that I won't need to because my left ovary will take over the hormone production, but I'm wondering how true that is. Also, I don't know if it matters, but I'm 40.

Thank you!