We were in Paris 3 years ago, when a general strike was called for the day we were ticketed to fly home from CDG. We had been told that, on general strike days, all busses and trains shut down, and taxis are generally unavailable.

We called Delta and plead our case to a supervisor, who rebooked us out of Brussels. We were able to get the Thalys high speed train up to Brussels and ended up having a really nice time, and had a good flight home the next day.

That might be what you'll have to do; leave Venice early, and take a 2.5 hour train ride plus a 1 hour bus ride to MXP.