Some soft leavers won't ever vote for UKIP. The idea of Brexit is going to change as well, from the fairytale that was sold to the actual reality.
They won't need the soft leavers, because for a general election they don't need 50%+ of the vote.
You're also assuming that the idea of Brexit will change widely if it doesn't actually happen, which I doubt. Many will put it down to scare-mongering, as we didn't actually Brexit, so how can X/Y/Z be Brexit's fault, etc.
The question is, in those circumstances, could UKIP win a majority in a general election?
That I don't know, as it depends much more on the geographic distribution of seats against 'Leave' voting areas. I would hope not, but I feel that would depend on Labour providing a strong united opposition for Remain voters to get behind.
If UKIP get a majority, the first order of business would be Article 50, 'backed by the 2016 referendum and the recent GE mandate' (GE mandate being as little as 25%+ of the vote!).
To be clear, I want absolutely none of the above to ever happen, but reading articles trying to persuade people that the Conservatives can duck out of Article 50 without mentioning political consequences beyond that point is something of a joke.
