How long are magic cards actually "printed"/"In production"
I cannot speak towards any product printed and packaged for general consumption (ie. booster boxes, theme decks, special sets such as Planeshift or Commander, and Fat Packs, among others), but Wizards does list redemption guarantee dates for sets redeemable from Magic: the Gathering Online.

From their Magic Online Product Release &amp; Redemption Schedule:

As a general rule, Magic Online sets will be available for redemption roughly one month after they are released. If a redeemable set runs out of stock before its Redemption Guarantee Date, the set will be reprinted. After a redeemable set's Redemption Guaranteed Date has passed, such set will be available while supplies last or until its Cutoff Date, whichever comes first. All cutoff times are 9:00 AM.

At the very least, it appears that Wizards will print new product at least until approximately one month after a set rotates out of the Standard Format (if the initial print run is not sufficient to meet the Magic: Online redemption demand.)