In my league games I have added the following item to the TDA rules as an addendum:
Player Leaving – Where a player leaves the TD shall remove their chips if they are satisfied they are not returning. Where there is uncertainty they shall remain in play, A player will not receive final table points if they do not return before two players are remaining in the tournament.
For games involving cash, I think I would prefer to have a stipulation where 2 complete blind levels elapse, any chips still in play of an absent player shall be removed from the tournament.
Stuart