If anything, the alcohol will kill off or inhibit bacteria/fungi. If you didn't know, 70% ethanol solution (of course this isn't even close to 70%) is often used as an antiseptic. Also, that combination of cranberry and orange juices seems pretty acidic, although that won't totally stop bacterial growth. Why not play it safe and keep it in the fridge for the same length of time you would keep an opened container of orange juice.