I had been in that situation recently.
I had to postpone my trip to Germany due to personal issues to a later date. I cancelled my ticket four hours before the departure. Fortunately, I had travel insurance. So I got the ticket price refunded.
If you have travel insurance and you miss your flight, then you can file a claim under trip cancellation or curtailment.
Most of the insurance companies refund you the difference in airfare or a percentage of airfare depending on your situation if the cancellation is due to an accident, or unavoidable circumstances like a family member falling ill, or travel difficulties due to unforeseen natural calamities (bad weather is not usually covered). It varies from policy to policy, and mostly you would be reimbursed if unforeseen circumstances occurred 30 minutes before the flight departure.
If you have no travel insurance, then you have learnt an expensive lesson at the cost of a new flight ticket.