I gather you want to hear about real live people's stories of what happened when they went off their homone treatment.
There is a woman here in Perth who was on Tamoxifen for 6 years after a chestwall recurrence that was removed surgically. That recurrence appeared 22yrs after her initial cancer and mastectompy with reconstruction.
She is ER+ (estrogen receptor positive) and HER2+ (HER2 receptor positive) Because of Tamoxifen side effects, when she got to 6 years, her oncologist gave her the choice to stay on it or come off. She chose to come off. Less than 6 months later she got sick and they found she had a dozen golf-ball sized metastatic cancer in her lungs and liver.
She then needed paclitaxel chemo again and is on Aramase Inhibitors permanently to deal with the ER+ bit, and herceptin to deal which the HER2+ bit. I heard that almost all of the metastatic tumors had gone after another 6 months, and she is expecting to get better and to get on with life. She said because she was ER+ ,once she went off her Tamoxifen, there was a hormone rich environment that let the tumors grow. And because she was HER2+ they grew quickly.
Is your Mum HER2 positive as well as ERpositive? because if not she is probably not nearly at the same risk as this lady. And if she is HER2 positive, has she had treatment with Herceptin or Perjeta or both? because this lady had not, so the HER2 had never been targetted. Even so, her oncologist was extremely surprised that she got this recurrence. I understand it doesn't happen often
But also, let your mum know that people can often get good treatment for recurrences that keep them alive and living well for many years. Or even, like this lady, probably cure them.
From the other answers from members of the network, t sounds as if your Mum's oncologist is not up to date, or maybe thinks her side effects are bad enough for it to be better to take the risk and lose the side effects. Perhaps she needs to get a second opinion from a more up to date oncologist. If you say where you are, maybe someone can suggest oncologists they know who might help.