The only feasible vacation setting in this light is the following:
The player enters the time he will be away and enters a message. Then, everything by this user will be suspended in the period he entered, with a maximum of, say, four weeks per year. This user cannot log in during this period, and cannot log in until this period is over. Also, the games will be suspended, so the timers will not run further and the opponent cannot claim the game.
This way, the player cannot abuse it by putting on his vacation settings and go play anyway to prevent claims. Furthermore, by applying a maximum (per year) the player cannot uphold any tournament or clan challenge for more than the alotted period.
Of course, as with any proposal, there are loopholes (which I will not mention
), but it is more watertight than the setting is now.