Knowing when Someone will die

Question

There seems to be an idea that it is possible to be able to divine when a person will die. The Chizkuni mentions (on Vayikra 16:21, "בְּיַד־אִ֥ישׁ עִתִּ֖י הַמִּדְבָּֽרָה׃ ") [from sefaria]

“by the hand of a man especially (temporarily) appointed for this task.”According to a Midrashnot found) the word: עתי, “which could be translated as: “whose time had come,” this is someone who was destined to die before this year is out. This would account for the fact that it was noticed that the man who had been entrusted with this task never lived out that year. [A well known commentator, author < of k’lee yakar, written several hundred years after that of our author, by the name of Shlomoh Efrayin ben Aharon, quotes this commentary, but attributes it to our author. Ed.] We must assume that in those days people used astrology to determine who was not destined to live out the year.

In Esther, 1:13, the Malbim comments that the men who were "yod'ei ha'itim",

היו יודעי העתים רוצה לומר שהיו בקיאים בחכמת המזלות

though he doesn't connect the mazalot to death, one of the ones named is Memuchan, whom the Gemara in Megilla 12b identifies as Haman, and Haman was an astrologer (http://www.koshertorah.com/PDF/purim.pdf page 5). So there seems to be an idea that one can figure out when someone is suitable for death or when one will die.

If that is the case, then what value is there in praying to be inscribed in a "book of life"? If someone knows that X will die this year, wouldn't it be better to let X know this (in fact, one could suggest that being chosen to be the one who accompanies the se'ir into the wilderness might be such a notification)? But then that would contravene Kohelet 9:12 כִּ֡י גַּם֩ לֹֽא־יֵדַ֨ע הָאָדָ֜ם אֶת־עִתּ֗וֹ .

This is supported by Shabbat 153a (via dafyomi)

(Mishnah - R. Eliezer): Repent one day before your death. (m) Question (Talmidim): One does not know when he will die! (n) Answer (R. Eliezer): Therefore one should repent today, lest he die tomorrow - this way, he repents every day - "B'Chol Es Yihyu Vegadecha Levanim v'Shemen Al Roshcha Al Yechsar".

Are there any sources which discuss the idea of others' knowing when a person will die and how that should affect how he is dealt with, or how he should behave?

Answer 1

אמר לפניו רבש"ע נסתכלתי באיצטגנינות שלי ואיני ראוי להוליד בן אמר ליה צא מאיצטגנינות שלך שאין מזל לישראל מאי דעתיך דקאי צדק במערב מהדרנא ומוקמינא ליה במזרח

‎Avraham said to HaShem, Master of the Universe! I've read the stars, and I am not destined to have a son. HaShem said to him, go out from your astrology, for astrology does not apply to the Jews. Why do you say thus? Is it because Jupiter is in the west? I will move it to the east. (Shabbos 156a-b)

Whatever an astrologer sees in the stars is how things may be now, but not how they must remain. Avram was destined not to bear children. HaShem told him to ignore the stars. He would change them to his favor. At some point in the future he would indeed bear a son - nine, in fact (Yishmael in Bereishis 16, Yitzchak in Bereishis 21, and Keturah's seven sons in Bereishis 25), as well as possibly a daughter (disputed in Tosefta Kiddushin 5:14).

The above Gemara in Shabbos brings three cases in point: that of Shmuel, who predicted - correctly - that the Jews destined to be killed by snakebite would survive (in the merit of their charity they ended up killing the snake); that of R' Akiva's daughter, who, in the merit of feeding a pauper whom everyone else was too busy to notice, accidentally poked out the eye of the snake that was supposed to kill her on her wedding day; and that of R' Nachman bar Yitzchak, who, as long as he davened for success and kept Yiras Shamayim on his mind, would overcome his natural tendencies to steal.

So, to more directly answer your question. If one is slated to live for, say, 50 years, he is able to extend that if he merits or diminish that if he does not. The fact that his fate today is to die then does not mean he must remain that way tomorrow, for better or for worse.

(By the way, this general principle is stated explicitly in Rosh Hashanah 17b. Tefillah works even after one's fate has been decided.)