A Dance With Dragons
Castle Black provides the horse to Val when she leaves on her mission to find Tormund Giantsbane. When Jon Snow goes to see Val off he sees the shaggy garron and is incredulous that Val has been given a horse that is blind, but Mully remarks that he is only half-blind and sound enough.
Val herself is unconcerned that the horse is half blind, telling Jon that she knows where she must go. After Val and her escort pass underneath the Wall Jon Snow bids goodbye to her. She then mounts the garron and wheels him towards the north.
At Alys Karstark and Sigorn's wedding feast a horn is sounded twice, announcing wildlings. Jon knows that Val has succeeded in her mission, and that Tormund Giantsbane has come at last. There is no mention of the fate of the half-blind garron.
You have my thanks, Lord Snow. For the half-blind horse, the salt cod, the free air. For hope.