Suggestion for Our Last 30 hours in Italy?

Just go to Milan and see something in Milan (Duomo, Galleria VE2, La Scala, Castello Sforzesco, etc) then have dinner along the Navigli. The next morning before heading to the airport, you could try to see the Last Supper (you need advance reservations).You don't have time for much else.
Remember that if you leave from MXP, the airport is far, but the Malpensa Express train can take you inside the airport from the Cadorna station in 36 min (or 52 from Centrale). Avoid the taxis to Malpensa. The taxi fare is huge (I think almost 100 euro vs. 10 euro on the train).

I would also suggest simply staying in Milan and seeing the Duomo &/or Last Supper, etc. If you had 2 days, I would have suggested Lake Como but it doesn't seem worth while to schlep to Lake Como for just 1 day. Have a great trip.

I agree. There are sights in Milan that will fill up a day most pleasurably. The best part of the Duomo is to go up to the roof and wander around, admiring the carvings and occasionally the view as well. Then walk through the mall (Vittorio Emanuel II), the very first of its kind . . . even the McDonald's is almost elegant . . . past the statue of Columbus in the little park and you're at LaScala, tour the theatre and the museum. Another few minutes' walk and you will be at the Castello Sforzesco, impressive in itself and housing several museums.

And the Castello Sforzesco has extensive grounds, great way to relax before your flight home.