"It was but a simple jest ,a jibe to entertain my guest."
You should have turned that into an Elder Tree reference from DAO.
Devs: "Leliana's survival will be explained in DA:I."
Leliana: "The Maker did it."
No, the ashes did it. The ashes can basically heal any injury, and she died within feet of it. Is it so hard to imagine it somehow healed fatal injuries over the course of a year? Even healing a missing head? The ashes are rather powerful. Of course, the real reason is because they've been absorbing super pure lyrium for literally ages.