I think it is a case of be careful what you wish for - the government collapsing would not halt Brexit. Ironically, officially calling a halt to Brexit is only likely to make matters worse... the day when Brexit could have been halted more easily has long since passed... a call to halt Brexit now would force a General Election and could see a resurgent UKIP (or a newly forged right-wing 'populist' coalition) take power. But even if that is unlikely, it could merely pave the way for an even more Euroskeptic Tory party to take power, perhaps with the support of a populist coalition. Even a Labour landslide would not halt Brexit now.
As has been said in the past, what the majority of UK people (and MPs) want - a soft Brexit - is not possible. It has been utterly rejected by the EU at every opportunity, and the EU will never accept it. Therefore staying in or a complete break with the EU are the only credible options left, but both options are politically very difficult, if not impossible, to win full support for. As such, it is looking more and more likely that the outcome will be the closest thing possible to the current 'default' option, which is to crash out of the EU without a deal, as there is no political mechanism, agreement or will within the UK or, crucially, within the EU27 to stop it - Brexit could only be reversed by universal agreement to restore the status quo prior to the referendum, and that isn't going to happen.
If the UK announced a second referendum was to be held before March 29th, and the British people voted to reverse Brexit, then it would, in effect, be folding its hand and be forced to accept whatever new terms the EU27 agreed to between them - and that could include anything from removing Britain's rebate to demanding that the UK's current opt-outs (on the Euro, Schengen etc.) are also withdrawn. Of course, if that were made clear before the vote, the chances of a win for Remain would be practically nil... so it would probably come as a nasty surprise after the vote was held. Of course, this would be cited by Brexiters as enough of a reason to call another referendum!
If the vote happened after March 29th, then the UK crashes out by default and would have to apply to rejoin the EU, and that would be 100% guaranteed to involve losing every opt-out (and the rebate), plus a commitment to ever closer union - something that I don't think will ever win a popularity contest in the UK... in other words, once we're out, we're out for good. The trouble is, though, that the status quo - i.e. our current deal with the EU, is already gone, even if we do manage to reverse Brexit, because, crucially, Article 50 can only be reversed by agreement of the EU, who can pretty much demand whatever they like from us in order to allow us to stay in.
My money's on Rees-Mogg, sadly.
Mine too.
if/when Dave Milliband steps up
I'm still shocked that Ed Miliband beat him to become Labour leader - Sadly, Labour has been a train-wreck ever since.