How could Zimri be Shelumiel?

Question

After mulling over this question for a bit, I realized that there's a big problem with that Gemara quoted there. Shelumiel is listed back in Bamidbar 1, before the sin of the Meraglim. By the time the stories recounted in Balak happened, everyone from the previous generation had died. How, then, did Shelumiel Ben Tzurishadai survive that he could commit the sin with Kozbi?

The decree of the generation dying ended on Tu b'Av (Taanis 30b). Aharon had died fifteen days earlier, on Rosh Chodesh Av (Bamidbar 33:38). It was some time after that that Sichon and Og attacked at the end of Chukas (RH 2b makes clear that this happened after Aharon died) and it was as a result of Klal Yisrael's astonishing victory that Balak sent for Bilam (Bamidbar 22:2-4). When that plan failed, Bilam advised him with Plan B at Shittim (Rashi to Bamidbar 25:1) which resulted in the sin of Zimri and Kozbi (Bamidbar 25:6, 25:14-15). Thus, there is no room to say that the parshios are out of order, or that not everyone had died yet at this point.

Answer 1

Rabbeinu Tam (Tosfos Bava Basra 121a 'yom shekalu') suggests that 15,000 people who were originally supposed to die during the last year were spared (including Yehoshua and Kalev). Shlumiel could very possibly have been among them.

Answer 2

According to Rashi, peshuto shel Mikra (the actual meaning), there's nothing that points to him actually being Shlumiel ben Tzurishaddai in the literal sense (in fact, the opposite is implied when Rashi mentions that he was the head of only one family) and seemingly the Gemara in Sanhedrin (82b) is seen as Agadeta. Aggadeta is not necessarily the posheter peshat, the exact meaning, and it could well be that he learned from Shlumiel (similar to Yehoshua being an extension of Moshe), who in turned learned from (or was) Shaul bas Dinah.

The Yalkut Reuvaini explains that Zimri was a gilgul of Shechem and a spark of Zimri later became Rabi Akiva, so there's another source that would lend credence to Zimri not actually being Shlumiel Ben Tzurishadai, a Tzadik.

However, from Bamidbar 14:29 and Rashi there, the gezaira (decree) on the Dor HaDeah to pass on in the wilderness, it seems that the decree only applies to those counted, those who were between 20-60. If Zimri was as old as some commentators say, this would answer the question.

Edit: Here's a source that backs this up.

From the Shem MiShmuel who clearly says that Zimri had parts of their (Shlumiel Ben Tzurishadai and Shaul Ben Shimon/Dinah)'s souls in him.

וכנראה מה שנלכד זמרי בפח, אף שהיה אדם גדול נשיא בישראל, והיו בו עוד נשמות גבוהות מהקודמין מהשבעים נפש שירדו למצרים, שאול בן הכנענית ושלומיאל בן צורישדי, שקאי על הנשמות, שרחוק לומר כפשוטו, שהרי עברו כבר יותר מר"נ שנה, ועוד שכבר כלו מתי מדבר, ואף למאן דאמר דלא מתו יותר מבני ששים, תצטרך לומר ששלומיאל כשנתמנה זקן היה, מה שאין כן במשמע, ובודאי הפירוש שקאי על הנשמות, ואולי היה מעותד לתיקונים גדולים, ובאו נשמות אלו לסייעו, אבל נתקלקל לו הענין, ונלכד בפח... ונראה שנמשך זה מחמת פגם ההמון, שידוע שההמון פוגמים את הצדיקים וצריכין שמירה יתרה,