Whilst I don't have metastatic disease, all of us when faced with breast cancer diagnosis think about stuff like this.
So I say...do what you love. If you thrive by working and it makes you feel mentally great and not physically too taxing...why stop? If you feel you need to work a bit less due to tiredness...then look at that. Lots if work places will accommodate that.
There are other treatments after ribociclib, so even when it stops being effective that doesn't mean that's it.
Working on bucket lists can be helpful. So...if you want to see the pyramids...have that holiday. It doesn't mean you have to do it all now...finish work because you think you should rather than want to. Great holidays take money...so working and regular breaks can be the perfect combo.
Small steps. You'll know when the time is right to finish.
We all have shitty days. ..that's what sick leave is for. Or having a short break.
My sister lived 10 years with metastatic disease. She and her husband bought an ostrich farm. She volunteered at her grandkids kindergarten so she got more time with them....she did this right up to last few weeks. She thrived on being busy and useful. Something I suspect you do too.
Kath x