If MN adjusted a federal item that the IRS hasn't caught yet (such as failure to report a 1099-R as income, or incorrect reporting of self-employment wages) then you should also file a federal amended return and pay what you owe. Any interest and penalties for unpaid IRS taxes will continue to grow until it's paid, and if they catch you later it will just make the penalties more.
(On the other hand, the IRS only has 3 years to audit you from the date you file or the filing deadline, whichever is later; or 7 years if you under-stated your tax by more than 25%. So if you want to roll the dice and hope the IRS doesn't catch you before the statute of limitations expires, that will at least make your daily walk to the mailbox more interesting.)
