Generally, I say their character is too busy with his seasonal actions to be bothered coming to the latest party/adventure. If the players were in the MIDDLE of an adventure and the player couldn't make it because of Work/Family/Health then I have them knocked out/flee/do something that removes them from the adventure but doesn't harm them in the long run. The same if it's a frivolous reason, but with ramping up penalties if they miss again and again.
I tend to want my players to play and if they can't commit to a regular night every week/every other week like it's a bowling league or something, I don't feel the need to keep them in my game. There are plenty of other players out there.
"Forbearance is the root of quietness and assurance forever. "
~ Tokugawa Ieyasu ~
Calaban Ru ~ Evil, Back-Stabbing, Serpent Marquis who has died!
Thane soon to be blooded as ~ Zsanosz Steele ~ A Gentleven's Gentleven and valet to Lorr Silja.