Fair enough. If I already knew there were two it would work for me. But if you just said "There was a terrible fire. Karen was the only one to survive" would you not expect more than one casualty?
Yes, but as much because of the 'terrible fire', which suggests something large enough to kill a lot of people, as of the 'only one'.
I have to admit, however, that if the incident is put in a slightly different way, I approach your way of thinking:
There was a fire at 37 Postule Road last night, and one person died. (We have no idea how many people were in the house).
There was a fire at 37 Postule Road last night; one of the two residents died. (not 'only one')
There was a fire at 37 postule Road last night; only one of the residents survived. (There were more than two)
The more I think about this, the more I think that I am not making sense, even to myself. :shocked!: