the tribe will leave me behind on the next migration when I'm too old and weak to keep up.
FWIW, this part is almost certainly not true.
https://news.usask.ca/articles/research/2017/ancient-spinal-injury-a-story-of-survival.php
These are just a handful of these types of stories, there's loads more if you want to search for them. But the upshot is: your family or tribe would have taken care of you to the best of their ability, for as long as they could, and you would have been given a decent burial when you died.
I don't know, but apparently people had some way of managing.