If these are award tickets, then they would be able to be cancelled and miles deposited back for a cost of $150

If these are normal tickets, then it really depends on the fare rules as to what is permitted

The cheapest revenue one way ticket seems to be R class $3615 plus taxes and charges with the cheapest round trip being $3450 plus taxes and charges

If the cheapest fare, then there would be no refund - looking at more expensive fares , even the $6000 D class fares seem non refundable . Getting to R class $6600 and there is a $400 penalty for refunds - if you have purchased one of these, then may be able to get refund of $6600 - $4015

Unless you did purchase flexible tickets, then you can throw them away, but not likely to get anything back

Is the effort of taking a bus worth more than the price of new one way tickets back?