I've had the injections twice, once with HRT add back (livial) and once without. If you're having them without then yes, you are likely to have hot flushes and some other side effects, but TBH I didn't find it unmanageable and it was better than the bleeding and pain. It helps to go in to it with a positive mindset if you can.
I've also had a hysterectomy and had endometriosis shaved off my bowel. First off, the hysterectomy part (removal of uterus) will only help if you have adenomyosis. I also had my ovaries and tubes removed (this is a BSO) as evidence shows that having your ovaries removed with the hyst reduces the chance of the disease returning. However, this puts you instantly into an irreversible surgical menopause which has long term detrimental impact on your health. There were various reasons why I had the hysterectomy - I already had children and definitely didn't want more (husband had already had a vasectomy, and the endo had damaged my fallopian tubes, so I was most likely infertile and even if I had wanted more children, the realistic chance of getting pregnant was very small). I had adenomyosis. I had extensive bowel disease, and rectovaginal endometriosis, and my consultant advised that if I just had this excised, the scarring would stick my uterus and bowel back together making a hysterectomy inadvisable if I needed one at a later date because of the risk of permanent damage to the bowel if it was operated on again. None of the drug treatments had worked, and I had experienced pain and bleeding on absolutely everything. I had reached a point where I could just about manage to take my kids to school and that was it. The bleeding was so heavy I frequently had accidents, I was struggling to cope with the level of pain I was experiencing and it was making me frightened and anxious, and my consultant basically said the only reason not to have it would be if I wanted more children. I think if you're ready you know because you're sure. However, I would not have considered it if I hadn't been absolutely at the end of my ability to cope because it is a horrible surgery and although being menopausal at 39 is better than the state I was in beforehand, it's still hard.
Hope this helps. x.