You speak as if the two questions being voted on are identical. They're not.
The first question was, should we Remain exactly as we are, or should we Leave in some totally unspecified fashion? The second question will be, should we Remain exactly as we are, or should we Leave in a no-deal hard exit, since that's the only possibility still on the table? It's no longer an abstract Leave, to which everyone can ascribe all their dreams and wishes; it's now a very specific Leave, with all the faults thereof. That may change the voting somewhat.
And, down the road, if there's another concrete Leave on the table, should the people have another referendum? Sure, why not? There probably won't be a need to vote on the negotiated Leave, though - losing by 230 votes in Parliament is probably enough. And there won't be any need to vote on a hard Brexit a second time, either - if it's voted on in a referendum, it will lose 65-35 or 70-30. (Or so I suspect, but what do I know? I'm not in the UK.)