Once your cruise is cancelled, if a credit is offered, Disney will automatically roll it over to the credit for future use in the timeframe they give you. If you want a refund, they will do that up to 100% of what you paid (not the total on credit, if you were given more). If you book a future cruise, you will have until the normal PIF for that cruise to cancel and get your money back.
In my case, I booked all of us on a cruise for next March because it was selling out and there was no other date that worked for us. I have until next October to change my mind and cancel all or any one of the members in my rooms.
As for it "not being fair", tell me how it's fair that my son, who is off to university next year and thus has a differing schedule from the rest of us, will have to cancel because we can't use ours in the summer (our 15 months expires in mid-June). A July or Aug cruise would have allowed him to go with us. A May or June cruise means his high school brother can't cruise.
We all have circumstances that are not convenient. And can I say, how is it "fair" that my son will be missing his prom and convocation because of a "shelter in place" order for the rest of the season and may actually miss out on the rest of his education? How is it fair that he might lose out on a lucrative spot on a university sports team because his skills are wasting away? How is it fair that people who are healthy are dying within 2 weeks of getting this "thing"? And how is it fair that we are all worrying about our loved ones and their safety, not sleeping at night because we don't know how we will wake up - healthy or sick?
Nothing about this virus is "fair". We are all making choices to the best of what we can, including Disney and
DCL. If the credits won't work for you, take the refund and rebook for when you can travel. You won't be out any money, just the bonus "deal" you would have gotten with the credits.