If this car is like other modern fiat transmissions, you dont have a true throwout bearing or slave cylinder. They are combined onto one part. Essentially I hydraulically actuated release bearing.
Your clutch pedal having no prssure and not returning is typically a hydraulic issue. Also, I'd say it's rare for it to just happen once and then function normally. Since your a mechanic, it should all be easy for you. I'd check the car over for leaks in ckutch hydro and monitor fluid level. These hydraulic release bearings seem to be the reason for clutch replacements these days before the actual disk ever wears out. It's also kind of annoying for owners that it replaces the slave as this is typically an cheap, easy part to replace. Not so with the hydro release bearing.