Anti-theft system light is flashing and will not start?

If you still have the pieces you can get a key made on a non-transponder blank and then take the plastic head and hold it with the new key in the ignition and it should start. Or have them cut the replacement on a transponder blank, then wrap the new keys transponder head in aluminum foil and use the old keys head to start the vehicle, then you can at least drive it to a dealer or locksmith and avoid the towing or a mobile service fee.

However you will still need to visit a locksmith or dealer to be able to program in the new transponder key(s). Ford requires 2 good programmed keys to be able to add any others and you only have one.
I would opt for the locksmith as they are generally cheaper than a dealer, especially on older vehicles. The advantage of doing it this way means you still can use the same locks and ignition switch. The other option would be to replace the ignition cylinder to get new keys. Then you still need a locksmith or dealer to program them in because of the way the system operates so you spend more money to achieve the same result.