airlines do not changes the passenger name on a ticket for one simple reason: if they did, a lot of people would buy tickets in the name of "john/jane smith" well in advance, then turn around and sell the ticket to someone else for a higher price, then have the name changed. this is unfair to the airlines, and so no name change is allowed, period.
besides, if your ex-wife is going to leave and not come back, she will do that regardless of anything you can do.
it would be much better to let her go and see what happens, she will respect you more that way.
You CAN NOT change the passenger names on tickets once they've been purchased. I would suggest you make the effort to get them refunded, or exchanged as you will be wasting your time trying to get them to change the name. NO AIRLINE will change the name on a ticket. Sorry.
Airlines do not allow a name change on an airline ticket. Your best bet, if you are worried like you mention, is to cancel the ticket all together. That they will do for you.
it's normally a 75.00 charge for a name change, but that's if its booked through the airline. If purchased from an internet provider (priceline, orbitz, expedia, etc) they won't allow that kind of change.