Under what circumstances can the new Brexit extension (31 Oct) be ended short of that date?

The EU has said that:

If the withdrawal agreement is ratified by both parties before this date, the withdrawal will take place on the first day of the following month.

The BBC also reports that:

The UK must now hold European elections in May, or leave on 1 June without a deal.

Is a no-deal scenario before the 31st of October really a possibility?
Are there other circumstances – apart from ratification of the withdrawal deal in Parliament, and not organising EU Parliament elections – under which the UK might leave the EU before that date?