Couple of faults spring to mind. Coil as you've already said (even the early ones can cause failure - rare though). Replace coil, plugs & leads. The most common however, is wiring loom corrosion to the ECU, due to windscreen or poor scuttle/bulkhead sealing. Not an ECU fault as such, but will cause problems if not checked properly. I think there are a few instances in the archives of Fiesta wiring loom problems.
NOTE: (Of course, it could just be a "poor" repair has been carried out, and the first quote was in fact correct - "the ECU is irrepairable" without it possibly coming back)!