What happens if Parliament rejects May's Brexit deal?

“The government is counting on some Labour MPs to save its bacon. There are half a dozen Eurosceptic ones who may well vote in favour of May’s plan. There is also another small group of Labour MPs who are less Eurosceptic but worry about annoying their anti-EU constituents by being seen to try to thwart Brexit. The government hopes that other, pro-EU Labour MPs will be ‘responsible’ and vote to avoid the potential chaos of no deal. But the government seems unlikely to win the backing of more than 10-15 Labour MPs. Even if a number of others abstained, May appears to be heading for defeat on the meaningful vote.” (Charles Grant, Centre for European Reform)