Those closer to the industry would probably know more, but from what I have understood from many past postings, you risk the cancellation of all subsequent sectors - or the airline potentially billing you for the full fare cost of all sectors. You get a RTW fare at a special price - a contract from the airline to you. You breach the contract and you might be liable for full fare on all sectors. Wouldn't it be easier to re-issue the ticket and pay the USD75 fee?