There is another little subtlety that is easy to overlook. What was agreed last week was that May's deal was this:

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(2) agrees that, if the House has passed a resolution approving the negotiated withdrawal agreement and the framework for the future relationship for the purposes of section 13(1)(b) of the European Union (Withdrawal) Act 2018 by 20 March 2019, then the Government will seek to agree with the European Union a one-off extension of the period specified in Article 50(3) for a period ending on 30 June 2019 for the purpose of passing the necessary EU exit legislation; and


(3) notes that, if the House has not passed a resolution approving the negotiated withdrawal agreement and the framework for the future relationship for the purposes of section 13(1)(b) of the European Union (Withdrawal) Act 2018 by 20 March 2019, then it is highly likely that the European Council at its meeting the following day would require a clear purpose for any extension, not least to determine its length, and that any extension beyond 30 June 2019 would require the United Kingdom to hold European Parliament elections in May 2019.

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What is easily missed is that clause (3) applies if the negotiated agreement has not even been put to MV3. Couple this with Hammond's statement:
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"We will only bring the deal back if we are confident that enough of our colleagues, and the DUP, are prepared to support it, so that we can get it through parliament. We’re not going to keep presenting it if we haven’t moved the dial," said the chancellor, Philip Hammond.

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and the likelihood of asking the EU for a long extension increases significantly.