Proper etiquette would be to stay with a mission team until completed or until all members are dead. An outpost would be the desired and courteous time to exit a party.
Things may happen which prevent you from completing a mission and leaving abruptly. These situations are not prevalent and not a problem.
Some people do leave out of spite. That's unfortunate, but to be expected in an anonymous internet community. It does make it more difficult on the others to complete a difficult and long mission and that's a bit unfair.
Others leave because Mommy said no more GW for the night and they got caught going back to finish that last mission. That is also unfortunate, and the results are the same as the spiteful dropper.
If there was a way to see the number of times someone unpartied outside of a town or outpost, it would compel people to display more common courtesy or else be ostracized or outcast and greatly alleviate the aforementioned problem.
I would also like to apply the same logic to /deaths. It would be helpful to know the caliber of a player beforehand. This is not intended as an elitist smear. Some people I've partied with refuse to follow the aggro rules of the game and just attract mob after mob only to die every time and spam "rez plz." That ..errr..playing style

should be reflected for others to see, like an online caveat.
In addition, major computer crash problems should be addressed, not whined about on the forums. Your continued partying with others is as selfish and detrimental as the reasons listed above.
Just some thoughts.
PS. How do
you know that most people have a legitimate exuse for dropping because you feel you have one??
