I'm a bit confused what's being asked here;;
If no commission is delivered, then of course the money should be refunded. If the commission is done but took a long time, then no refunding is needed but apology would be nice ofc, and giving an extra sketch, etc. would be a nice gesture. If you're struggling with a commission, you can say to the customer that you can't do it and refund the money, or deliver the results and think about how it sits with your morale to charge full-price from a half-assed job.
From a customer point-of-view, if you're taking a long time with a commission, please, let the customer know. I'm a patient person, but waiting like a month with no word from the artist just sucks.