Given various alternative scenarios the UK may decide to follow in the short amount of time left until the 29 March deadline, here how things could pan out.

After the UK Parliament voted down the Withdrawal Agreement on the future relationship between the UK and the EU on 15 January, Theresa May's government has been facing the challenge of proposing a different deal. The new proposal has to get the approval of both the House of Commons and the EU 27 to become a viable solution.
Alternatively, if no deal is struck, Britain risks exiting the bloc in what is known as 'hard Brexit' on 29 March 2019. Source: sputniknews.com