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://www.sciencenewstoday.org/these-4000-year-old-bones-reveal-a-shocking-secret-about-humanitys-earliest-caregivers

https://www.npr.org/sections/goatsandsoda/2020/06/17/878896381/ancient-bones-offer-clues-to-how-long-ago-humans-cared-for-the-vulnerable

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.