The prime minister said she will put her withdrawal agreement – including any changes she has agreed with the EU – to a meaningful vote by 12 March.

If that fails, MPs will be offered two separate votes:

One, on the following day, on whether MPs support a no-deal Brexit – so the UK would „only leave without a deal on 29 March if there is explicit consent in the House for that outcome“
If that fails, then MPs will get a vote by 14 March on requesting an extension to the two-year Article 50 negotiation process to delay EU withdrawal beyond 29 March