Otdfbt

Upfront: this is a metaphysical/theological question

In many (almost all?) areas of Jewish practice, there are a number of different and at times diametrically opposed opinions as to what the practice should be. Even if say that all opinions are true (eilu veilu) in some sense, we can only do one thing in practice, and hence one of the opinions is chosen to be halacha lemaase [of course different individuals/groups may choose different opinions as their halacha lemaase, as decided by the posek they ask].

My question is - after 120, does G-d care that we followed the halacha lemaase, and as long as we did that in good faith, we're ok as far as judgement and reward/punishment goes? Or perhaps He cares that we follow the right opinion (the correct truth, if such even exists), and so those who followed the wrong practical opinion would be in trouble?

As an example, one person carries outside on Shabbos while his neighbor does not, because the former takes as his practical halacha an opinion deeming the eruv as valid, while the latter's posek says it's invalid. Will they both be judged based on their faithful observance of what they thought was the right view, or will they be judged based on the correctness of only one of these views?

Shabbat 130a

ת"ר במקומו של ר"א היו כורתין עצים לעשות פחמין לעשות ברזל בשבת במקומו של ר' יוסי הגלילי היו אוכלין בשר עוף בחלב לוי איקלע לבי יוסף רישבא קריבו ליה רישא דטוותא בחלבא לא אכל כי אתא לקמיה דרבי א"ל אמאי לא תשמתינהו א"ל אתריה דר' יהודה בן בתירה הוה ואמינא דילמא דרש להו כר' יוסי הגלילי דתנן ר' יוסי הגלילי אומר נאמר לא תאכלו כל נבלה ונאמר לא תבשל גדי בחלב אמו את שאסור משום נבלה אסור לבשל בחלב עוף שאסור משום נבלה יכול יהא אסור לבשל בחלב ת"ל בחלב אמו יצא עוף שאין לו חלב אם א"ר יצחק עיר אחת היתה בא"י שהיו עושין כר"א והיו מתים בזמנן ולא עוד אלא שפעם אחת גזרה מלכות הרשעה גזרה על ישראל על המילה ועל אותה העיר לא גזרה

Our Rabbis taught: In R. Eliezer's locality they used to cut timber to make charcoal for making iron on the Sabbath. In the locality of R. Jose the Galilean they used to eat flesh of fowl with milk. Levi visited the home of Joseph the fowler [and] was offered the head of a peacock in milk, [which] he did not eat. When he came before Rabbi he asked him, Why did you not place them under the ban? It was the locality of R. Judah b. Bathyra, replied he, and I thought, Perhaps he has lectured to them in accordance with R. Jose the Galilean. For we learnt: R. Jose the Galilean said: It is said, Ye shall not eat any nebelah, and it is said, Thou shalt not seethe a kid in its mother's milk: [this teaches,] that which is forbidden on the score of nebelah may not be seethed in milk. Now since a fowl is prohibited when nebelah, you might think that one must not seethe it in milk; therefore it is stated, 'in its mother's milk', hence a fowl is excluded, since it has no mother's milk.

R. Isaac said: There was one town in Palestine where they followed R. Eliezer, and they died there at the [proper] time, Moreover, the wicked State once promulgated a decree against Israel concerning circumcision, yet did not decree [it] against that town.

(Soncino translation)

It seems from this passage that the people of R. Eliezer's town were judged favorably, even rewarded, for following his ruling even though his ruling was rejected from the accepted corpus of halacha.

In my approach, G-d follows the Gemmorah in Berochos 17aת i.g. follows one's heart:

אחד המרבה ואחד הממעיט ובלבד שיכוין לבו לשמים

Once G-d declared "נצחוני בניי" in R' Eliezer and the Rabbis' argument (see B"M 59b), He allowed the Rabbis to develop the Halachah anyway they like.

If we still assume that G-d does care for the fulfilment of the Torah commandments, we should remember that all Rabbinical decrees, Halochos, rulings, Minhagim, etc, all stem from one Mitzvah of following the rulings of the Supreme Sanhedrin "ועשית ככל אשר יורוך" (Rambam Mamrim 1) which was further modified into "following Rabbis", in general.

So as long as a person follows a Rabbi's rulings it appears he'll be fine with the Heavenly court as he could claim "who said Rabbi X is better than Rabbi Y?". Or if he truly believes he's a Tzadik (acts solely for the G-d's sake), he can follow "וְצַדִּיק בֶּאֱמוּנָתוֹ יִחְיֶה׃" and follow his own conclusions (that's what Rabbis themselves do).