try setting out bait-esque things
like catnip, catfood, water, etc
if he's ok he'll have to find water eventually and i'm sure he'll come back to the 'safe' spot he knows of when that time comes
trust me, setting out things like that and waiting (looking doesn't hurt) is a really good decision, my snake got out multiple times (like when he was smaller then a shoelace) and setting out a heat pad, his moss and water got him back every time