maybe they really and ultimately narrowed it down to "gone".

also they ruled out:

• up or down
• sideways
• back or forth in time
• with the wind
• hiding
• just vanishing
• gone for good
• gone for a walk
• other realities / timelines / simulations (maybe recovery from backup is still possible)

...

8-)

UPDATE-edit: damn i forgot Schroedingers quantum gone paradoxon: He decides where he was only in that very moment when they actually find him.