If you paid with a credit card (or gift card, etc.) for the flight and cancel, you need to retain that confirmation number to apply the travel funds to future travel; the new travel must be completed within one year from date of original booking. If you had EBCI, that value will be lost. There is no voucher involved, so keep that conf. number in a safe place.
Flights that are booked with RR points and cancelled are much simpler. The points will be returned to the original account, and the taxes and fees will be credited back to your credit card. There is no time frame, whatsoever, involved with a points booking. Just be sure to cancel the flight before departure.