A victory by the team seems 'within the realm of possibility'. [=a victory seems possible]
It's not 'beyond the realm of possibility' [=it's not impossible] that he will return.
new discoveries in the 'realm' of medicine
(..) until your force is mine to command, you are but words. You will have your war, Asgardian. If you fail, if the Tesseract is kept from us, there will be no realm, no barren moon, no crevice where he cannot find you. You think you know pain? He will make you long for something sweet as pain. (..)2012 The Avengers