I'm not sure why the tournament format matters.
But I agree that since the player paid for his seat, unless he is disqualified or specifically states that he forfeits, then the stack should play out.
If the absent player eventually cashes, lock up his winnings the same way you'd bag the chips of an absent cash player.
If he never returns to inquire, do whatever you'd do with that cash player that never came in for his bagged chips, or unclaimed slot TITOs.