If I understand it right, the song was recorded weeks BEFORE the accident, so it's not like the KURSK submarine disaster, where a Russian crew was stranded at the bottom of the sea and might have been rescued if only help from Britain would have been accepted earlier. So it's sad but unfortunate. Singing soldiers stranded at the bottom of the sea, that would be creepy.
I don't think anyone assumed that this was recorded after the accident? For all we know those unfortunate people passed immediately.