In Bang! When the Bone Orchard is still active, can the player return to the game many times or just once?
Yes, you can return to the game multiple times while BONE ORCHARD is in play.
Like a lot of rules in Bang! this is covered in the original Italian rules but was left out of the English translation.
Luckily the publisher has this covered in their English FAQ under Q21.
Q21. If I come back in play with Bone Orchad and I am killed again, if the Bone Orchard is still in play when it is my next turn, do I come back in play again?
A. Yes, you may come back into play at the beginning of each of your turn while the Bone Orchard is play