Players connot join the party while you are engaged in combat

[Physic]

Well you could disengage from the monster and run away, then add the person, it only takes like 20 seconds to leave combat if everyone disengages. And monsters dont have instant regen, it takes awhile before they begin to regen hp back.
You would lose sp/exp for attacking it with less hp, but for experience mobs, its one kill, and for NMs you re generally looking for the drop over the exp anyhow.

When someone Dcs,
either kill the mob then add the person
disengage and run away then add the person and re attempt.

The connection lost on an NM is the only real reason its a problem imo, and disengaging while not perfect would work in that situation 99% of the time.

I do like the definitive answer (well as definitive as we re going to get anyhow) that was given, so now you can either take it or leave it, the system is as it is.

[Physic]

i was opposed to invites to party while engaged from the start. , while i could see the DC being inconvienient, there is a solution. Spending time trying to solve all the issues with keeping hate, disconnecting and reconneting to the same data, querys showing in game and what not, is a waste of time imo, when you could just disengage and re invite. Getting DCed sucks, but thats life.