Here's a what-if scenario for you all...
Let's say we vote Leave. Cameron steps down next year, which leaves Boris as a shoo-in for the party leadership. Nothing will happen on leaving the EU on our side until then, so that gives Boris three years as PM. Now, he'll most certainly want to carry on being PM and win the GE in 2020, so how best to achieve that? Certainly not by alienating voters on the Left any more than he has to, given they'll already have plenty of ammo aimed at him. His own party will back him and he's adored by UKIP voters too, so no fear of annoying them regardless. So how does he win the centre-Left? Well, one way could be to make some nice concessions to the EU in terms of the withdrawal agreement and/or trade negotiations. Just enough to keep the Left not completely hating him, but not enough so he looks weak.
Now I like Boris, and I'd love him as PM, but he's also incredibly shrewd and clever. He'll do whatever it takes to keep hold of power, and he won't rock the markets any more than he has to to achieve his goals. I'm not saying this is a guarantee, but at the same time I don't for one second expect him to keep a hardline over this. Political suicide.