I think you would need to check against guaranteed train list. My understanding is trains won’t run from Milan central To Malpensa so only book train to Milan Central. How much are you paying for the Rome to Milan leg? You might be better to fly from Rome to Milan Linate which you can get for...
i’ve just decided to book flight from Rome to Milan with ITA Airways flight at 12:00 on Friday cost us £45 each, allows us about 3 hours to get from Linate to Malpensa. Didn’t want to risk, train not running. Hoping I can get our money back for the return train journey that was booked.