The referendum was something like 51% for to 49% against confederation with Canada. There was only 2% in it. I wonder what the exact number of people who would need to have their minds changed would actually be?
Perhaps some sort of faux pas by Canada that damages relations with Newfoundland? Perhaps the Canadian government might bring up the border dispute between Quebec and Labrador again? To be honest though it looks like by 1948-49 London was not convinced that Newfoundland could ever be a viable dominion.
An interesting alternative to consider might be a Newfoundland directly incorporated into the UK. Since the nearest part of the UK is Scotland imagine Newfoundland being administered as a distant bit of Scotland? Would be amusing to imagine the Newfies all having to drive on the left.
Not a particularly likely outcome but I do like thinking about the possible implications.