Why just the $10k? Could you get a full refund? If I order a $12 burrito and you give me a $10 sandwich, I would feel owed my $12 back, not the $2 difference in price.
You should have the option of getting the $12 back provided you also return the sandwich. You don't get a free sandwich out of the deal unless the seller cares about good will.
The reimbursement covers the add-on. It's more like ordering a $10 sandwich and a $2 bag of chips, then not receiving the bag of chips and getting your $2 back.