Check out Hystersisters.com, they were an amazing help when I had mine.
My hand was forced at the time, I had a large (think the size of a pomelo) complex ovarian mass. Everything came out as one scarred block.
It took a while, but now, a few years down the road, I feel so much better than I ever did. I went without estrogen for a time but now use a bio-identical patch at a low dose and am happy with my results. My hemoglobin was 8 by the time I had my surgery; it turned out I had stage IV endometriosis, giant endometrioma with possible "borderline" cells, and severe adenomyosis.
I had Rebecca at age 40, (I turned 40 the week after she got home from the NICU) and after an ectopic and miscarriage, and severe pre-e/HELLP. Getting pregnant again would have been a VERY bad idea for me.
I realize there is a wistfulness to the thought of never experiencing pregnancy again (along with the death of the hope of ever having a "normal" experience), but you will be a healthier mother for your daughters, I bet, once this is in your rear-view mirror.
Do your research. I moderated over on HS for some time, and one thing that came through loud and clear for the endo ladies was the fact that the disease made surgery much more difficult than it would have been for less complex problems. If you can, have your surgery done by a GYN-oncologist. They are much more experienced at removing every scrap of disease.
Hopefully you can have a laparoscopic procedure (LSH maybe). The down time for that is much much less than the "standard" more drastic procedure that I had. I was able to keep my cervix, and that's another question to research.
I'm sorry it's come to this for you, but for most of us, we're healthier without organs that are that diseased. Just my own experience and that of others. Not everyone gets a great result with endo, but I can tell you I am much healthier than I was (mentally, too, without the insane moods I went through month after month). Good luck, and let me know if I can answer any questions (although I'll be off-line for the Jewish holiday, back by Sunday).