I believe that on UA it's use it, CANCEL IT, or lose it. If you call and say you won't be using it -- even if you don't figure out what your new itin is and if you don't pay a change fee -- the ticket will stay OPEN. If you just plain no show (and don't call that day) it will convert to ZERO.

Originally, most airlines required you to confirm something new (and pay any associated change fees/additional collections) prior to the originally ticketed flight, but many backed away from this and simply require notice that you won't be flying.