The 50m (not that many - see Khol's reply) had their chance and blew it, and I say that as someone who voted remain and thinks this whole thing is a disaster, and leaving either with the May deal (bad) or the hard way (worse) would both be worse than staying. However, the people had their chance and they voted to leave. That's how democracy works. It's a serious business with real consequences.
If there is a new referendum it should be about the terms under which we will leave, and that's all. Yes the May deal is crap, but any deal we cut with the EU was going to be a horrible fudge. So much for 'cutting a deal with the EU will be the easiest in human history' because 'we hold all the cards'. I have nothing but sympathy for Theresa May. She's made mistakes, sure, but anyone else would have made their own mistakes.