I just get my parents passports extended today for my parents (NY Consulate). Their visas have also expired. You only need a valid entry proof, rather than a valid visa at the time of extension. They didn't ask for the visa.
If you wait until they expire, it can be quite troublesome and costly to get new passports. This is important if you want to apply greencard for them in the future. So you should do it ASAP. Good luck.