I have done some research. If the airline cancels your flight you are entitled to a refund to your method of payment. When this first started airlines tried to give e-credits instead. DOT stepped in and "refreshed" their memory that a refund has to be included as option. So in your case you pay of pocket will be refunded to your credit card and the Skymiles will be credited to your Skymiles account, if you want a refund vs an e-credit.
Also if your original flight departure/arrival changes by a certain number of hours, they are also required to give a refund if you request it. I am not sure of the number of hours.
Right now airlines are allowing people who bought or were scheduled to fly during certain time frames to cancel for an e-credit or reschedule the flight with no penalty. They have extended the time before the e-credit expires, in Delta case from one year to two years. Right now you don't qualify for this.
So basically you have to sit on your hands to see if policies I refer to in paragraph are change as we go forward.