Though I've never flown RTW discounted tickets using logic I'd say this falls into involuntary rerouting.

A carrier sold you a ticket with a certain numbers of legal itineraries which in the one-year time frame allowed by contract they ceased to exist. The passenger accepts to be involuntary rerouted to another airport/carrier to continue its journey/contract.

I've had this happen with deep discounted Y tickets (though with a reservation) and with UA award open return tickets and I've never been charged a dime.

Shouldn't you call a different CTO (in another country) that can be more reasonable and accomodate your needs ?

[This message has been edited by pb9997 (edited 06-07-2002).]