If your flight is cancelled, you are entitled to choose between these options:
A refund of the ticket price within 7 days, covering the full cost of the ticket at the price at which it was purchased, for the part or parts of the journey not made, and for the part or parts of the journey already made, if the flight no longer serves any purpose in relation to your original travel plan, together with, where applicable:
A return flight to the first point of departure as soon as possible.
These rights are recognised in Regulation (EC) No 261/2004 of the European Parliament and of the Council, which establishes common rules on compensation and assistance to passengers in the event of cancellation, denied boarding or long delay.