On your first point, surely that depends on the turnout and the margin of victory? If only 45% of people vote and the vote goes 51/49 to leave, does that give Johnson et al carte blanche?
Interesting thought. I don't know the answer. I suspect the turnout will be higher than the last general election, so will trump the Commons in terms of legitimacy.
I'd be surprised if the turnout is anywhere close to general election levels. The Voting system referendum saw a turnout of just 42%. The last EU referendum, in 1975, saw a turnout of 65%. I'd think tomorrow will be somewhere between the two.
General elections usually see turnout at around 70%.
On your first point, surely that depends on the turnout and the margin of victory? If only 45% of people vote and the vote goes 51/49 to leave, does that give Johnson et al carte blanche?