There are seceral rules here that need to be considered:
9. Face Up
All cards will be turned face up once a player is all-in and all betting action is complete.
39. Unprotected Hands
If a dealer kills an unprotected hand, the player will have no redress and will not be entitled to a refund of bets. However, if a player had raised and the raise had not yet been called, the raise will be returned to the player.
22. At Your Seat
A player must be at his or her seat by the time all players have been dealt complete initial hands in order to have a live hand. A player must be at his/her seat to call time.
For the purposes of a TOURNAMENT where the player is present, I would not kill the hand, instead would table it and let the best hand win as per 9 (even where that player is not at the table/seat)
For the purposes of a TOURNAMENT where the player has been absent for some time, or has not been present from the commencement of the tournament I would have the dealer touch the cards into the muck before tabling the hand in order to comply with 9.
With regard to your situation, if I was satisfied the player was not returning I would kill the hand before tabling it, but if he was on tilt after a bad beat etc, I would likely leave the hand live as he was all-in and table it with a view to claiming the pot if it is the best hand. It really is one that can go either way and will be at your discretion, there is certainly no right or wrong asto how you handle this situation.
Regards
Stuart