I would suggest that BrExit would merely be a convenient scapegoat if we voted Leave. Leonardo seems to be repositioning its assets, wherever possible, back in Italy (which should come as no surprise as the Italian govt is a major shareholder). If the UK MoD is not the sort of customer that is going to order another 30 Merlins or 40 Wildcats, and seems certain to go to the OEM for Apache this time, then why should they keep a plant in the UK open? Merlins and AW139/49/68/89 can all be built in Italy or the US, the A609 is nowhere near Yeovil. The only platform solely built in the UK is, I think, Wildcat which is only getting a handful of orders. Maybe post Apache some MoD "sweeteners" will be forthcoming (taking the Option on the other Wildcats to replace Lx 9A / Gaz perhaps) or, perhaps, there will be a double header in Tory nightmares; a massive split over Europe and a revisiting of the Westland crisis. Only this time, selling to the US would probably be a good thing.
Tourist - I agree; the designers I know at AW are amongst the best in the world. Every time we've given them an aircraft they've improved the breed. The problems are with some very short sighted marketing people and some poor choices of workshare to keep / develop certain technologies in Italy.