If something is happening in my life where I can’t use my airline credit within a year, I’ve got bigger issues. Even then at least with Delta, you just have to book a flight using the credit before it expires - and the flight can be after the credit would have expired - wait 24 hours cancel the ticket and then receive a new credit that resets the timer.

Or ask customer service to extend the validity period. YMMV, but this worked for me the few times I tried.