Boy, that IS a tough one.
Guesstimating how long someone will live is a little like predicting when a baby will actually be born.
The passage seems to be on it's own timetable on either end of life. It can come earlier and it can come later. And not alot you can do to predict!
I do know how you feel about the chemo. Dad was in clinical trials and seemed willing to do them right up until it just wouldn't have been physically possible without an ambulance. He also had radiation but only for palliative reasons since the cancer had spread to his hips & spine.
The radiation was ok, but man, that chemo (for a Stage 4 patient) is pretty rough in my book.
You certainly have your plate full. One of those mixed blessings I am sure. I know that it is REALLY important to look out after yourself. Your Mom certainly fits the major criteria for Hospice and they are there for YOU just as much as for her...
And, it IS entirely possible that your Mom will hang on to her physical life right up until she decides to let go. (like her grandchild's birthday!) But either way, I can just about assure you that she'll be at that party in spirit if nothing else.
I hope that you'll keep in touch so that I can kind of walk a ways with you and your Mom. It would be nice to hear about your Mom, what kind of person she is, what she did, etc. Maybe later?
Take care of yourself - meals - sleep.
Hospice can help.
Don't I sound maternal for someone who never had kids!