Had a similar situation happen to me with NW.

You can cancel the ticket, and apply the price of the ticket to future travel. You will have to pay the $75 change fee, but only once.

They gave me up to 1 year to rebook another flight, BUT I don't have to use up my entire $1200 in one flight. When I book my next flight, they will give me the difference in non-transferable/non-refundable travel vouchers. I then have 1 year from that point to use the vouchers. I will only have to pay the $75 fee once.

Now, this is how it was explained to me on several seperate occasions by NW customer service. If anyone has a different opinion, feel free to reply!

[This message has been edited by mat123 (edited 06-01-2000).]