Right so i've read eveyones thoeries and have come up with a sort of mixture

Dd knew about the plot and he and snape had a plan so that lord voldemort would think Dd was dead.

this brings us to the top of the astronemy tower, the culmination of the plan, snape shouts "Avada Kedavra" just after he has non-verbally performed another curse. thus making the surrounding death eaters think he has killed Dd. Dd then falls back and drops down of the tower, still alive, somehow cusioning the landing. If you remember the person who removed Dd's body was hagrid. Say he was in on the plan and had instructions to switch the bodies for a fake one. Dd can then escape and the fake one is then buried, again an elaborate charade so that people beleive he is dead. So we presume he is in hiding and as is said in book five, (haven't got it to hand so not an accurate quote) "i examined him for his transfiguration OWL, did things with a wand i've never seen before. If dumbledore doesn't want to be found, he won't be" Owl Examiner

thats my idea, any thoughts????

either that or he is dead and were all just in a severe case of denial

*Harry's secret Brother*