Normally, when you travel overseas, you purchase a travel insurance policy for the period for which you will be abroad. However, if the duration of your stay abroad gets extended due to an emergency and the airline asks you to rebook your return ticket for a future date, then in such a scenario, you can extend your travel insurance for a limited time period.
If the cancellation is made from the airline's end, then they will bear the cost of your new flight ticket. But, will your insure ..