I've had to change the ignition switch on three Fiats, one wouldn't actuate
the starter, one locked up mechanically and wouldn't turn at all,
even after WD40, RAC lifted the front and towed it a couple of miles, well
they had to as the steering was locked. The other one cooked the switch
contacts, no relay, so headlamps, heater motor, rear screen heater,
wipers, and just about everything that comes on with the ignition goes
through it. Fiat use several mfrs. so it's a case of pot luck as to whether
you can swap the contact block. Replacing barrel is a pain in the butt,
due to the awkward location and snap off head bolts, job to get the drill
centered. Can't see how these bolts help security in any way, so
fixed replacement with ordinary bolts. Of course replacing the switch
means one more odd key, worst case, one for the doors, one for the
ignition, one for the filler cap. If it is intermittent sods law dictates it
won't happen when it's with the garage. To check Ignition switch I'd
jury rig 12V bulbs on the switch outputs, then if it's the switch one
will go out.  Not sure about your model but there may be protective
devices and well hidden impact sensor switches that do things like
fuel cut-off and kill the ignition on impact. Had a case where a relay in
this setup was intermittent, took a guy who had worked for Fiat to
(after may had expensively tried, and failed) to find it. ECU readout
showed nothing. Dealers working on intermittents, by trial and
error, gets expensive, sure it's electrics ??? The little neon gizmos,
that go in series with a plug, are invaluable here, to see if the plugs
are getting a spark. Personally I use a timing light, brighter flash,
easier to see in daylight. The simple ones only cost a couple of quid.
You can of course bring a lead through one of the bulkhead grometts,
and put a 12V bulb on the feed to the coil, if that one goes out and
everything dies, work from there, back towards the Ignition switch.