In the second season (and afaik, series) finale, Will is thought to have sacrificed his life to undo the warlock lord's corruption of the world- but near the end, when the elfstones glow in Mareth's hand she realizes Will is alive somewhere.
In the final scene Will wakes up in a bleak landscape with humanoid skeletons half-buried in the dirt around him and winged monsters flying in a black, starless sky above- where is this place?