You are entitled to a 2nd opinion under the NHS- and as many other opinions from any gynae if you pay and get a drs referral.
I would not do anything until you have had at least one more opinion and ideally two- I am constantly amazed at how different consultants have different views, and how many are out of touch.
I had a benign ovarian cyst and my gynae followed a " watchful waiting" regime- scanned every 3-4 months. Eventually it went away. He said that he was 98% sure it was benign. In time he said it was def not cancerous.
He also told me that cysts can turn cancerous- they either are, or are not.
None of the treatment you have had so far is for cancer- you have had endo and a dermoid cyst.
I cannot see why the dr wants to carry out such a radical operation- it's a bit like a woman being offered a mastectomy because she has benign breast cysts (though sometimes benign there can mean more at risk from malignant.)
I think this sounds draconian. Ovarian cysts are very common as is endo.
It is not true that you do not need your ovaries after meno- they continue to produce a small amount of estrogen right into your 70s and 80s, and also testosterone.
Toothbrush what you have said about ovaries being symtomless when cancerous is not correct. Ovarian cancer always has symptoms- a cyst- and when more advanced, other symptoms caused by the tumour pressing on other organs. It can be over looked, and if women ignore vague symptms they may not be diagnosed until too late, but it's not right to say there are no signs of ovarian cancer.
OP- I'd ask your GP for another referral.