Our Gemara on Amud Aleph tells us about a man who accepted upon himself 365 consecutive Naziriyos, (30 days x 365). Upon his completion of this cycle he passed away. This story brings to awareness the idea that sometimes a person may be living off the merit of a particular mitzvah or purpose, and if he stops, it could be the end of the line. Similar to an old brick wall that was held up with dirt and moss in the cracks in the place of cement. If you clean it away, the wall starts to crumble. This is a thought provoking idea, that if one has a particularly meritorious practice, even if conducted bli neder, there is some danger in dropping the practice.
There also is an idea that each person, or even creature, has a mission. When the mission is completed, then there is no more need for physical existence. Kad Hakemach (Yom Kippur 1) makes this observation about the fish that swallowed Yonah. According to the Midrash, upon spitting Yonah out, it died. It was a miraculous creation to begin with, and thus completing its purpose, it had no further reason for existence.
My father Z”L died Erev Rosh Hashana, within a few minutes of finishing giving his class at Azrieli Graduate School of Education. Being niftar at the close of a year, seems to suggest as well this idea of a mission completed. Indeed, his mentor for the last 40 years of his life (a reclusive Adam Godol whose identity was kept secret for many years at the Rav’s direction) was also niftar in a similar manner many years prior, on Erev Yom Kippur. Personally, I am not keen on the idea of leaving this world, whether missions are accomplished or not, however it is a comfort to think that there are some about whom it can be said, “Job well done!”