3.5 Hours to Kill in Rome (9:00am - 12:30pm)

Is your Sardinia flt at 1230 or 230?

Even at 230 you really do not have time to do much more than dash to/from and grab a pannini.

Enjoy a glass of wine, or 2, at the airport

Have you seen Ostia Antica? It's about 12 km taxi ride from FCO airport. It opens at 8:30 am. If you haven't seen it, it's a wonderful archeological site.

My husband and I land at 8:10am in Rome and don't fly out to Sardinia
until 2:30pm in the afternoon.

If Rome/Fiumicino is your first entry to the Schengen - meaning you have to go through immigration - I would say that you really don't have time to do very much. Certainly not to go into central Rome and back. Ostia Antica by taxi might be your best bet but I wouldn't arrange anything in advance in case your flight is late.

Stay at the airport....who knows if you will even land on time...

You don't have to decide now. See how it works out. Your luggage will be checked through to Sardinia (I assume) and you will have your boarding passes. So when you return, you only need to get through security and get to the gate. There are local trains to Rome every 15 minutes weekdays, less on weekends. You could get to Trastevere in 31 minutes, walk around and have lunch. If you land on time and get through immigration quickly, might be doable.

I agree with a previous comment to wait until you get there before making a decision. Your flight could be late, there could be a large queue at Passport control or other problems that affect the amount of time you have available. Don't underestimate the effects of jet lag, and how tired you might be feeling.

If your luggage is checked through to Sardinia and you only have carry on, you could perhaps walk to the Rome Airport Hilton and have a nice hot breakfast (and lots of coffee) there. The hotel is accessible right from the terminals.