Well the meaning of the veil is (like a thin fabick) is that we start out in the spirit world which seperates us from the spirit world, which we can only be brought thu by first choice and then an earthly mother, but nothing I have found says that it has to be human so I have trerory that he could be brought back by being reborn thru another magical creature, how ever I do not think that this is what JK is going to do.
I believe that he is going to try an speak to harry from behind the vail. thru his dreams or something like that.