I have a wire that is bonded to my upper front four teeth. A few weeks ago the last tooth came "unbonded." What should I do?

I would find a dentist in your current location that will remove the remaining part of your retainer until you get home.  Once you are home you should find an orthodontist and have a new retainer  bonded in to keep your teeth from relapsing.  Good luck.

Sorry to hear about your unfortunate circumstance. It always happens at the worst times. If you can get to a dentist to have the broken wire removed or smoothed so it doesn't irritate you, that would be the best option. In the long term you will want to have a new one placed as the teeth can relapse into improper position without the wire to retain there alignment. I wouldn't recommend trying to cut it or pull it off yourself. You may hurt yourself in the process. If it is poking you there are products like orthodontic wax you can get at a drug store to place over the exposed sharp wire so it doesn't rub against your tongue and tissue. 

Go back to your dentist and have him rebond it. This will make it stronger and do what its supposed to do.