At some point in history, ない replaced *あらない as the negative of ある, at least in the Kantō dialect (Kansai seems to have あらへん; あらん is also apparently attested in some dialects).
When did this happen? That is, when did なし and its descendants replace あらず and its descendants? Were なし and あらず coexistent in the Heian period, or was one preferred over another? I see both used in later CJ texts, but it feels strange that there are two words with exactly the same meaning for such a common idea (not exist).
Currently, in polls etc you often see あり・なし as choices, rather than あり・あらず. Is this a Modern Japanese influence, or is this usage idiomatic (i.e. なし rather than あらず was seen as the obvious opposite of あり)
Additionally, does なし and あらず have different nuances?