Seeing as the large-scale outbreak occured during the late night of September 24th 1998, wouldn't his death have occured then? A person infected by t-Virus isn't dead (desite their appearances), so Nicolas was alive until late that night, when the large horde of zombies (the same horde that attacked J's Bar) was destroyed via explosive charges strategically placed beneath the main street.
Going by that, Nicolas was most definetly killed on September 24th, 1998 in the explosion, had the group of survivors not killed him beforehand.
Regarding the second paragraph, I see how that technically works, as Nicolas attacks Eric when the barricade collapses, he is clearly present when "Mop-Up" is enacted.
Addressing the first paragraph, we're generally going by the dates of their human deaths, and however likely that may be that he as a person died on the 24th, it is, nevertheless, conjecture at this point. Like I said, it doesn't bother me either way, personally, as I believe in cases such as this a certain level of common sense presumption is necessary to establish likelihoods, such as safely assuming almost all of the RPD officers mentioned but not seen in the games are probably dead, even though there is insufficient evidence to prove that conclusively. Again, this isn't an issue for myself, but there might be a more strictly adherent editor further down the line who will pull you up on that. Cheers. Flare1983 (talk) 00:17, May 23, 2018 (UTC)