Translation:A lot of people passed away.
I didn't know this verb until I looked it up just now, so I can't speak from experience in how to interpret its usage, but nakunaru 亡くなる meaning "die" is written with different kanji from nakunaru 無くなる meaning "be lost, be used up, disappear". So I'm not sure that translations based on taking the former as a euphemistic use of the latter should necessarily be accepted. (On the other hand, since it's in hiragana maybe they should be accepted on grounds of ambiguity anyway.)
It is a euphemism. It is a much gentler way of saying that someone has died and translating it as "passed away" is absolutely accurate. 死 and 死ぬ are a very harsh and blunt of talking about death or saying that someone has died. Homonyms are "guilty by association" so to speak and their usage is to be avoided at all costs if possible - hence why words like the number 4 四 have bad connotations associated with them. Anyone who has lived in Japan will tell you that it is entirely normal for the number 4 to be skipped over as a house number, apartment number and even a floor number.
Good ques--- wait, didn't this say "a lot of people died"? I'm pretty sure it did. Did they censor it? Why?
Since "pass away" is an English euphemism, I would be surprised if this literally means anything about "passing". But it does look like it might be similar - my look at Google Translate (yep) suggests なくなる generally means to "disappear", "go away" or "become lost", but なくなりました is understood as "died".