The only way to be certain that you preserve the value of your tickets is to cancel. Anything short of that leaves open the risk that the tickets are cancelled and lose their value. It comes down to your risk tolerance. The cost of a toll-free phone call vs. whatever you paid for the tickets.

Just to be clear though. If there have been cancellations or significant time changes since the reissue which you accepted, you are entitled to a refund. You can then use those funds to purchase whatever you want and whenever you want. Or do something else entirely.