Estrogen substitution can't bring the endometriosis back, if the endometriosis was located only at the womb (uterus), ovaries and fallopian tubes (structures that were removed during your surgery).
I guess, you were examined for additional endometrial growths, that can be found on the lining of the pelvic cavity, the area between the vagina and the rectum, on the intestines or in the rectum, on the bladder, vagina, cervix, and vulva (external genitals).
There are uncommon locations of endometrial growths, like lung, thigh, lung and others.
If you are endometrial growths free, estrogen therapy won't cause you problems.
However, there is a small chance that your symptoms will come back even if your uterus and ovaries are removed.
Estrogen therapy is important for protecting you from other medical problems.