Could an MP say that enough is enough, ...

[Holidayshopping]

...they supported Remain and would be prepared to be the leader of the party (or a new party?!) and keep the country in the EU?

TM has got a crap Brexit deal no one wants. The alternative is JC (I used to actually like him!) who is saying we need a general election so that we can have his Brexit deal (which no doubt no one will want).

If someone stood up and said-‘I’ll be in charge, vote for me and we can cancel it and just stop and think about what the hell we’re doing’.

Would that even be possible?

Not really. A prime minister has to be capable of forming a government, or at least commanding a majority in the HoC to get their government's policy through.
As long as TM can still do that she is PM. If she loses a no confidence motion in Parliament (not in her party), I think there has to be another General Election. The next PM is whichever party leader can get a working majority of MPs in House of Commons.
They have to go to to Queen and say, I can command the support of a majority of MPs in Parliament and I will be your Prime Minister.
But we are heading for uncharted waters.

You need a majority for something. At the moment, the only majority is against something (No Deal.)

The UK can unilaterally cancel Article 50 and call the whole thing off, but an extension of Article 50 to facilitate another referendum (wart, a nutherr wun??) or general election requires the agreement of all the EU member states.

Basically, We're All Gonna Die....

{Basically, We're All Gonna Die....}

That is being too dramatic.
All but a very few are going to continue getting poorer and significant numbers are going to lose their jobs.
The decision on 29 March will simply define how much poorer and how fast.

If she loses a no confidence motion in Parliament (not in her party), I think there has to be another General Election.

They have 14 days to attempt to form a new government with the support of a majority of MPs. It is feasible (I've no idea how likely) that a cross-party 'revoke' (or pro-deal) government could be formed on a temporary basis to deal with this crap.

Has JC said what his deal will be and how he will get a better deal?

How is this expected to happen before March 29th?

Labour would stay in a customs union and so all the backstop stuff would disappear, but to get there you need to have an election, which needs an extension. Even then it is difficult to see Labour getting a majority, and the Nats will want their referendum as a price for support.

Another EU referendum is also a problem? What is the question? How many options? What about the franchise? (16-17 y/o's, EU citizens in UK, UK citizens in EU, dependent territitories beyond Gibraltar such as Anguilla etc.)

As David Aaronavich has pointed out, the rising new adults and dying oldies will have wiped out the Leave majority before May's transition period is up.

Given how bent out of shape some Leavers have got about the backstop, they'll be even worse about us staying in the single market and customs union under Labour.