And how would that work then? Surely you would need to keep the Lloyds Duo acount open to receive the cash refund when you eventually cancelled the refundable flight? And if the account is open, surely they would deduct the Avios originally credited when first made the purchase, leaving you with a negative Avios balance on the Lloyds account. And wouldn't they think that rather suspicious when you then tried to close the Lloyds account?

(All that aside, I think the morality (and possibly legality) is dubious, and therefore not something I would entertain doing except as a 'thought exercise'...)