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?