I did not know the answer to your question on St Lucia volcano death toll in the 1700's so I went to the St Lucia archives for some answers. There is no accurate records of the number of persons who died during the last eruption at the archives.
The St Lucia Archives holds all the information on the history of St Lucia so if they don't have that information, it is almost safe to say that there is no information on the number of persons who died there.
