People lingering, such as myself in pmdev, is messy. Putting in contracts like the one you stated, even if it affects everyone in the future, gives everyone the understanding that is their future is in their hands.
NB: When making timeout clauses, you may want to stipulate that reasonable, premeditated, communicated absenteeism may be ok depending on the time absent. 'cause you know, people get hit by trucks and what not. :)
Update: Well, jeffa is gone. Congrats.