It's my understanding that one can go in/out of remission a couple times before it becomes time for palliative care instead of continuing to fight. The doctors are not going to treat him if there is no longer hope of remission so I would hang onto his faith in his doctors' and live more in the moment rather than thinking ahead to how sad I am going to be later.

You could get run over by a car tomorrow and predecease him. We cannot know how long we have and eventually it will become common knowledge if he becomes that sick and everyone will be grieving/working together. That is not yet though so just work with what he is doing now and being with him now instead of preparing for a future you cannot know.