A bit late to the party and I won't comment on the substance because I'm not voting, but -
Springing I think you're being very pessimistic about the possibility of a second referendum. I'm starting to think "stay" may actually win (I have zero data to support my gut feeling), but I also think the Brexit debate would be far, far from over.
The major thing this referendum is doing is bringing Brexit into the mainstream of political discourse. Once it gets 45+% of votes, it will have become impossible to dismiss as the ravings of xenophobic tinfoil hat wearers.
And let's face it, the EU is not going to become a paradise of streamlined efficiency overnight, EU immigration would stay strong, and Britain would continue to have problems it can blame on the EU. So all the reasons behind the Brexit movement would continue existing.
If "stay" wins, the Brexit voters will be disappointed and up for grabs, and no way the Brexit Tories are letting go of this golden opportunity to run on a popular platform that may well get them power.
So while I think "stay" has a good shot this time round, I also think that mid- to long-term, "out" will have many political cards to play, and may well have its day.