Should your train be cancelled, you can take another train or opt for a refund. Here are the options for taking another train:
Take any next available train with the same operator (advance single tickets and anytime tickets only)
With off-peak or other restricted tickets, you must follow the conditions on your ticket
You can contact Trainline within 90 days after your train was cancelled to get compensated with a refund. Log into your account, go to your bookings and select the booking that was cancelled; there will be a button to request a refund.