Interesting questions, Dazbo (to which I do not, sadly, have the answers!)
It certainly is the case that Latin replaced most of the continental Celtic languages (eg Gaulish)under Roman rule - hence the Spanish, french, Provencal, Italian, Rumanian, and other less-used Romance languages extant today. Why did that not happen in Britannia?
And what would a modern derivative of British Latin look and sound like today?
Dáithí