Roy Mustang's vision was restored, so why can't Edward Elric try to use something to exchange back his gate, like using another philosopher's stone? Is it that he didn't need alchemy anymore because he fulfilled his wishes?
Remember that what Marco presented was his incomplete philosopher's stone which is somewhat unstable and can go off at any moment (i recall Marco saying this). also if i recall correctly Ed traded his ability to perform Alchemy for Al's life, i think if Truth was to give that back he would require a life and remember that neither Ed nor Al wanted to restore their bodies if someone else's life had to be sacrificed– Memor-XJul 4, 2016 at 13:32
2Note that Edward did not want to use a philosopher's stone to save Al, so it is doubtful he would have wanted to use one to get his alchemy back (were that even possible), particularly when his alchemy is less important to him than Al. I'm not sure if there is some deeper reason as well (perhaps it isn't possible in the first place to make such an exchange), but I'll think about it and try to write an answer later.– MaroonJul 4, 2016 at 17:21
@Memor-X: FWIW, Roy implies in the manga that he would have exchanged his gate for his lost eyesight. We also don't know whether the value of the gate is equal (and not greater than) Alphonse (or Roy's eyesight), particularly since it seems that there is some subjective aspect to what things "cost" in this realm, but this at least doesn't rule out the possibility that it wouldn't necessarily take a life in a hypothetical exchange of something for one's gate.– MaroonJul 4, 2016 at 19:50
Edward's actions when he recovers Alphonse indicate that he probably would not want to get his alchemy back, much less do so by using a philosopher's stone.
Ling offers Edward a philosopher's stone to use to recover Alphonse. Edward refuses because he and Alphonse had promised not to use a philosopher's stone (and more generally, human lives) to restore their bodies. Alchemy is surely less important than Alphonse is to Edward, so he would not want to use a philosopher's stone for recovering his alchemy (were it possible).
Edward tells Truth that he will be fine without his alchemy: he has always been an ordinary person who was not able to achieve everything he wanted, and even without alchemy, he has his friends. Edward accepts this result, so it would be unlikely for him to want to reverse it.
More generally, exchanging something for one's gate would probably count as a transmutation of sorts. If someone already gave up his ability to do alchemy, it would then seem contradictory for him to be able to exchange it back. (It is unclear whether another alchemist could initiate the exchange, but it seems unlikely in light of the personal nature of the gate.)
When Edward tried to transmute bricks (or something like that) at the end, he seemed to miss his alchemy powers though. Would he be able to use alkahestry then?– G.OleJul 5, 2016 at 4:58
I believe it would work if he had a Philospher's Stone. Remember the stone has the power of many human souls. Ed stated that every human is in fact their own Philospher's Stone, except each person simply has the power of one soul instead of millions. Ed gave up his gate as a payment to get Al back. A Philospher's Stone gives the illusion of alchemy without equivalent exchange, because it has the power of many souls, so using the stone would indeed get his back, or at least give him a brand new one.
Good point about the philosopher's stone giving the illusion of alchemy; if I'm not mistaken, Father Cornello does exactly that in the series. Note though that this isn't a route that Edward would be willing to take, and that it seems doubtful (at least to me) that Edward would be able to recover his gate either way.– MaroonDec 19, 2016 at 5:25